My z28 (87k miles) will shift fine, and pull hard all the way to redline, where then it wont upshift. During normal driving the trans shifts absoultely fine. What could be causing it?

 

morning bump...

 

I think... as your title states: your lt1 a4 is slipping

-Check your fluid level. If thats ok its time for a rebuild.

 

The transmission isn't capable of completeing the shift quick enough at higher RPMs. We get this complaint quite often when we get transmission in the shop. Fortunately, we know what modifications to make to provide a quicker shift and better transmission durability.
BTW, NO a shift kit won't fix this problem.

Frank
CPT