O.k here's the issue.
The basic specs: 700R4, G.M. crate 350 w/ TPI w/ 373 gears
I recently have noticed a shifting problem when in drive "D" and I floor it from a stand still. It accelerates to aprx 50 mph and the tack stays at aprx 4500 rpm not shifting into 2nd gear unless I take my foot off the gas to aprx 2/3 then it shifts into 2nd and the same problem happens again from 2nd to 3rd. Now giving it aprx 90% throttle at a stand still the same issue happens but there is a 1-2 second break / pause where the motor and the tranny stay the same as above but it shifts then accelerates unbelievably. It's almost like it thinks it's in o.d. and you floor it ( to the passing gear )and the only way you can get it to go back into o.d. to continue accelerating is to let your foot off the gas. Could it just be the shift cable on the motor has to be adjusted? or is there something wrong internally with the tranny??

 

Adjust the detent cable.

 

At full throttle it probably shouldnt shift until after 5k. If you have an engine problem it might not make the rpm to carry the shift. Check the tv cable, then make sure you dont have any issues with the motor.