Transmission question

['68 Short Step]

I'm trying to figure out if my torque converter is bad or whats going on with my transmission. When I first crank up the truck and drive around everything works perfect. After I drive it around for a while (20+ miles) the transmission starts to act funny when I accelerate hard or when taking off. feels like the transmission is sightly in neutral or something because the rpm's will go up but the truck is barely moving. After I get up to speed it's ok. Its a th350 trans. Thanks for any advice

[trac209]

Could be a number go things when it come to slippage. Could be a clogged trans filter,low fluid,bad clutches etc. check fluid level first and smell to see if it's burnt.

['68 Short Step]

Fluid is full and doesn't smell burnt. The filter is new. Not sure what it could be. May have to take it to a local shop and have them diagnose.

[truckdude239]

Time for a rebuild

['68 Short Step]

It shifts really well. I'd put a 700r4 in before I rebuild the th350.

[Longhorn 70]

Check filter first thing. I wonder if the governer is getting sticky or weights binding.

['68 Short Step]

I put a new filter on it a few months ago

[Longhorn 70]

were there any chunks in the pan? Did it immediately start acting funky or did it take time? Does it make any sucking nor growling noises?

['68 Short Step]

It was doing this even before I changed the filter. Nothing in the pan and no weird noises.

[Longhorn 70]

Very rarely have I seen a converter fail unless there is something catastrophic. Also they don't usually work then not then work again.

The governer is a more likely failure point. You can pull it from the outside and take a look. Sometimes they look like a chewed up apple core but still work.....kinda. I don't want to keep making suggestions and have you pour $$$ into it though with no results.

[RANZTRANZ]

If you think its the torque converter, does it do the same thing in reverse...you say it does it on take off, right ? if its the torque converter the same thing would happen in reverse I would think.... If it does not do it in reverse, I am thinking your forward clutches are burnt up, IMO...slipping issue normally is not caused by the gov....not to say its good or bad, I am not there driving your truck.....slipping on take off means to me that you are in first gear and has not shifted yet, so no point of gov/modulator issue yet...and not slipping during shifts right ? just taking off ? any clutch material in pan on your fluid change, did you put the gasket under the filter and tighten the two screws that holds the filter ? power brake the truck in forward and than in reverse...see when its breaking loose ?