at lower speeds, 30-40 mph, i can release the gas pedal and the truck begins to slow, and then it will seem as though the engine just disengages and goes to a complete idle and then if i give it gas the whole thing re engages. then today, in that same speed range, the truck started acting as though it were shuddering or shifting gears, but i didn't notice the motor speeding up when it was doing that. and the problem is completely random. i could power my way out of it or if i just steadily gas on it it wouldn't do it, just a steady speed or very lightly increasing speed.

i just changed the transmission fluid about a month ago. this problem existed before the fluid change(the motor feeling as though it were disengaging). i had hoped it would take care of the problem, but not so. i also drained the torque converter at the fluid change. the fluid level is full and looks clear and clean and does not smell burned. i used mercon v which was the recommended replacement fluid. the transmission is a auto 3 speed c6. when i pulled the xmission pan, there was a gray residue which i wiped out when i cleaned the pan.

thanks in advance!

 

The shudder sounds like the same thing I had going on in my old truck. It was the torque converter. I drove mine like that for about a year that way and it kept running. I eventually sold the truck and I see it driving around town still. No clue if it was ever fixed.

 

thanks. the more i think about it the more i realize that it really jerked the truck. today is the first time it has done that. someone else suggested the modulator could be bad. i pulled the vacuum hose loose from it and a small amount of transmission fluid came out of the vacuum hose indicating a bad diaphragm. it may not totally fix my problem, may be more than one problem going on here but at least i know for a fact the modulator valve should not have fluid in it. that will be one problem out of the way and with any luck, my entire problem solved.

 

Changing the fluid in my truck made the shudder better for a while. So my issue was slightly different from yours. I hope it something easier then the TC.

 

thanks! i don't think the modulator is the whole problem, but hope springs eternal.