I have a 2001 F350 7.3 and I also own a 2006 Bison Stratus 4 horse 12' short wall with a slide and I keep it out of overdrive when I am 50mph or less and in overdrive when above. I also have a transmission temp gauge and monitor that and the temp never exceeds 176 deg. when hauling on flat land. Sometimes I have to drop it back when climbing steep hills and I have the transmission fluid changed yearly and it never smells burnt or changes color.

It is like I always say "Ask 4 people a question and you will get 5 answers".  hehehe

According to my 2002 F350 dually manual:  Drive (without Overdrive on) provides more engine braking than Overdrive and is useful when:  driving with a heavy load, towing a trailer up or down steep hills, additional engine downhill braking is desired. 

I would imagine that the 99 F350 dually manual would state the same.

I have the same transmission and have temp gauges, so it's pretty easy to keep track of things. On secondary roads where the speeds are about 40 mph, I lock out the OD. If I don't, the transmission constantly hunts, shifting from 3rd to od and back. On the open road it's OD all the way. I set the cruise on whatever speed I want and let the transmission choose which of the two gears it wants. With my chip in its lowest setting, the truck infrequently shifts down to third, even on the steepest grades. Running synthetic transmission fluid, my max temp has never exceeded an indicated 165 deg F.

Running in third is a total waste of fuel, will add additional wear to the engine and accessories, and makes a bunch of unnecessary noise.

The computer will decide when you don't have enough power to make a hill, and automatically downshift the transmission for you. If the transmission isn't constantly shifting to adjust for your type of driving, use the highest gear you have. That will ensure the best economy and least amount of mechanical wear.

Gard

Synthetic transmission fluid?  I didn't know there were different kinds.  Is one better than the other for keeping the transmission cooler?

Amanda

Synthetic lubricants far exceed petroleum based oils in shear strength, longevity and most importantly, a resistance to failure under high temperature situations. They are the best lubricants available and will greatly enhance the long term life of any machinery in which they are used.

Our commercial airlines and military aircraft would not be flying without synthetic lubricants. Many automotive companies install these lubricants as an OEM product from the factory.

There are many differences in lubricants; choosing the right one will save you gas mileage and repairs.

Gard

I would want the gauges even if I didn't have all the other goodies. The EGT gauge and intake manifold pressure (boost) pressure gauge will tell you alot about how your truck is performing..... Even in the stock from the factory settings.

Checking the transmission is not the same as changing the fluid and filter. During this service the truck is put on a lift, the oil is drained and the pan is pulled. If you are considering the addition of a transmission oil temp gauge, this is a perfect time to install the bulb. A new filter is installed and things are reassembled. Checking the transmission is done under the hood with a dipstick.

You would have to request the synthetic transmission fluid. It is not an OEM product and costs considerably more than the petroleum based fluids. The only original fluid that was synthetic in my truck, was in the rear axle which is a limited slip differential. I had all the fluids in the front axle, transfer case, transmission, engine and power steering reservoir changed to synthetic.

I have never had any high temp problems with my chip in its lowest setting.(towing). The only parameter that changed much while using the chip, is the pyrometer which shows my exhaust gas temperatures do increase when pulling a load on long hills. My temperatures have never exceeded the max allowable. Under the same circumstances with the chip in the advance setting, I could easily over temp the engine, if I continued pulling maximum power for a length of time.

You may not need the gauges if you don't "hot rod" things. I was told a replacement engine was $10k installed, so I wanted to know what was going on while running, and I will do nothing that will cause a failure. If you were to buy only one gauge, I would recommend a pyrometer. It's a good thing you modified your exhaust. The original exhaust can be too restrictive if a chip is added and the exhaust is not opened up, to allow the engine to breath better. This can cause exhaust gas overheating that will damage the cylinder heads.

BOL  Gard

I have seen the Lucas additives and read their claims. Having never used the product, I can't accurately state if it's good or not. It is sold as a "friction modifier", presumably it lowers friction when mixed with oil.

That's the catch. It is mixed with the same oil you already have, so you're doing nothing to improve its temperature stability when greatly heated, or its longevity when used. The whole advantage of a synthetic product is its base product, which was designed in a test tube and not by dinosaurs. When using synthetic products, no additives are added or recommended.

I don't know of anyone who uses it, or anyone who has expressed any opinions, pro or con. I can state that it would not compare to the qualities that make synthetic oils so remarkable.

Gard