HELP...4L60e not shifting correctly...

[aggie91]

Alright, I am lost as to what is wrong with my swap. I put a 5.3 LM7 and 4L60e into my son's '82. We got it going in July and have put some miles on it, probably less then 500 miles.

Last week while I was out of town it started not shifting into 3rd gear for him and he limped it home. He checked the fluid and it was low, but no signs of a leak. He topped it off and just let it sit till I got home....

Anyway, I got back yesterday and took it out for a drive while he was at work. I warmed it up first and took an easy drive around the block to warm up the tranny. Checked the fluid level and it was full. The color is a bit dark, but not burnt looking and did not smell burnt. I took it easy and went down the road a ways. Here is what it does...under a moderate acceleration (about 1/2 throttle) is shifts thru the gears fine and even barked the tires going into 2nd. The converter locks up a little soon for me in 4th, but that could be a programming issue...I did a few stops/starts to get the truck into first and then run thru the gears again. Under very light to light throttle (1/4 or less) it goes fine thru 1st, shifts into 2nd and then when it is time to go into 3rd, it just free spins and the motor shoots up in rpm, backing off the throttle does no go to get it to go into any gear...you have to stop or manually put it into 2nd gear to get it to keep going.

What do you guys think it could be? The convertor we are using is a circle d 3200 stall. Like I said, it seems to work good under moderate acceleration, but does not work correctly under light throttle...It is his daily driver and school starts Monday and he needs the transportation...Any ideas??