hey guys,
88, 5.0L, C6 transmission with 200k miles on original tranny. Transmission fluid change and flush 50K miles back.

Problem: 25-30% throttle on accelerating, the truck will move forward at normal acceleration, taching bout 2500, and then the tach will drop to 2000 and the truck will feel sluggish, as if i am towing something, but the RPM drop instead of reving high.

these symptoms fluctuate not only under acceleration, but also while maintaining speed on the road (45-50 mph)

Questions:
is it slipping?-->i tend to think not b/c the rpm drops
is something bogging the engine down? -->maybe, but what? the engine runs fine and hold rpm when in neutral

any ideas?

 

Sounds more like a tuning issue than transmission. Unless perhaps the torque converter is locking up early.

 

As far as I know, the C6 doesn't have a locking torque converter of any kind. On another note, can auto trannies "slip"? I thought that was just a manual thing.

 

yes they can slip but in this case i would say its more engine related.

that 88 would be efi so pull codes.

also are you positive you have a C6 and not an AOD? AOD was far more common behind that motor.

 

Yea, I would think it was a AOD which I had in my 88'. If that is the case, shift directly to drive, NOT OVERDRIVE. Then if you get on the highway, shift to OD. When you get off the highway, shift back to drive.

 

my '88 had a C-6. Loved it!!! But mine was mated to the 5.8L FI