CHAIR-O-KEY89

I know that I have posted this thread before but Im giving it another shot for anyone to help me.

We just recently put back together my 89 Jeep Cherokee after installing a PaceSetter Header.
Everything is working fine, but for some reason its having a problem with the RPMs.

When cruising along at a steady speed, it shifts perfectly normal (2000rpm-2500rpm) but as soon as you down shift or gun it, it wont let the engine pass 2500rpm. It sits there like its hitting a govener and then will take about a minute to shift back to a higher gear.

I have no idea if it is a vacume line, relay or sensor. If anyone has ANY SUGGESTIONS what-so-ever; please let me know. I will try any ideas I get.

I am at a total loss for what it might be

builtnotbought89'

Have u tryed searching it???