I just finished swapping a ls1 4l60e combo in my 89 IROC. The problem I'm having is the transmission wont shift under heavy throttle. Any ideas?

 

Need more details... will it shift if you try it manually? Does it shift under part throttle okay? If it will shift automatically under part throttle while left in D or 3 but not under heavy, wide open throttle conditions, then chances are it's in the tune.

 

It shifts ok at normal driving either manually or in D. Tuner could not get it to change any different. When I say ok its still sluggish. Trans guy thinks shift kit is in order.

 

Would be curious to know what your "Shift times" are set to and pressures. Any idea how the transmission was shifting prior to it being swapped into your IROC?

 

Tuner is on vacation. Trans was rebuilt before installed in my car.

 

By "heavy throttle" do you mean WOT? WOT (typically over 96% throttle, but programmable) uses different shift tables that the partial throttle shift tables. If the WOT shift tables were way wrong, it might not shift.

Edwardzracing: Not to hijack this thread, but if you could explain to give a link to "Shift times", that would be appreciated. I know most other trans tuning tables, but have no idea what "Shift times" does.

 

Anything over 60% bad shift. Over 70% no shift without completely letting off throttle.

 

Tuner tried several settings results were same.

 

This sounds like the part-throttle shift tables are way off. This could be because the PCM doesn't know the speed of the car because the rear-end ratio is tuned incorrectly, the VSS is bad, etc.
Is your speedometer connected to the PCM? Is it accurate?
I would use a scanner (like HP Tuners) to view/log what speed the PCM thinks the car is moving at.

 

I have the same problem and i am my tuner. If i set the shift points for wot way low, then it will shift but if i set them to over 6100 rpm then it just blows right by it, hits the limiter hard. I'm very sure its not in the tune. A shift kit seems like a logical solution. I'm really considering a 4l80E for mine but its a heavy truck. I hopes you find a solution and post it up. If it does turn out to be the tune, that will be good news because it will be Ann easy fix.