DEX COOL, Transmission

Two Questions:
Have two GM cars in family. DEX COOL seems to have nasty habit of turning into gumbo on my cap, preventing the retreival of coolant from the resevoir. This in on my Buick 3800. Same stuff in the Montana no probs yet. But would like instructions on possibly switching to green stuff, as it seems the two are incompatable. maybe need a chemical to clean and flush in between.

Also do some towing. Wondering about principals of automatic trans. In towing it is often said one should not set in overdrive. Overdrive with the lockup I would think is preferable as it creates a postive connection btw engine and wheels. resulting in lower RPMs and better milage. I figure we are told to avoid OD to prevent excessive shifting and hunting for gears by trans. causing heat and clutch wear. Please someone give me facts about this not old what your grandpa used to say stuff. We wil be driving long distance next Sat so I need info soon. Thanks

Ovderdrive is more than the torque converter locking up. It is a higher gear ratio that is greater than 1:1, not sure what it is on the Montana. The whole concept of overdrive is for economy and not for torque. It will as you say cause more heat from shifting and also strain the transmission because of the high gearing.

Sounds like intake gasket for the mud on the cap. Oil and coolant mix.

The DexCool is actually pretty god stuff. It has lubricity additives to help maintian a closed system, and should be good for 5 years if no leaks.