Turbo 400 shifting issue!

[mattybilt79]

This is on my 85 CC dually. Last night I towed the 5th across az about 250 mi. Most of the drive was up hill in 80 degree temps. The truck really didn't enjoy it at all, temps were hot but below redline and just above 210 most of the way. The trans started taking longer and longer to shift to third after the few stops we made. I would have to speed up to 55 and let off then it would shift into 3rd. About 30 miles from the rv park the trans kicked down into second on a small hill at about 45 mph and then would not up shift back to third at all. Chugged it up the next hill in second until there was a place to stop and checked the fluid and it was below the hot line low reading. Dumped a quart of Lucas trans stuff it it and took off again and it shifted into 3rd the same way after letting off the gas but held 3rd up the next hill. When we got into town slowed to 30 mph speed limit then going out back to 45 mph and up hill again and no 3rd again. So I made it last night 10 miles in second gear! Checked the fluid this morning and its above the full cold mark, still have reverse but have not driven the truck yet. I'm hoping the modulator is going bad because I cannot afford a trans rebuild right now. I have only had the truck a few months and do not know the history of the trans itself but I did put the motor in. Was going to service the trans but got a filter that was smashed in the box and not use able so it never got done. Im pretty sure the kick down is still working and the 1/2 shift was still normal last night. So sorry for the long post but I'm pretty concerned here. We are 20 miles from the nearest town now but luckily have the Tahoe to drive. But this issue will have to be addressed soon. Any other suggestions?

[crashz]

We had a 86 dump that went through 9 TH400's in various fashions. Most common was overheating. How does the fluid smell? Is it dark? How about the vacuum lines?

The cooler in our 86 was in the radiator only, and when the engine warmed up it seems to cook the transmission. We never seemed to get to adding a large secondary cooler. The truck routinely ran at and above its GVWR with terrible drivers that drove it like a company truck, so its no surprise that it chewed up transmissions.

I'd drop the pan, change the filter, inspect for wear metals/particles, add a deep sump pan with drain plug, refill to proper level and add the red bottle of trans medic. If it starts improving, keep draining and refilling with clean fluid and add a big auxiliary cooler.