Something got mucked up in the process of reattaching the throttle cable/sensor. The tranny takes its cues from road speed, load, and throttle to decide when to shift. It's not getting correct information.
I imagine you're also finding it's upshifting rather early lately. Same cause - same solution.
It can be many many things..The bolts arent tight, the gasket is closing all the gaps, vaccuum leak, not broken in, TPS in the wrong holes, TPS not screwed down all the way, you forgot to hook up a pice of the intake...
I just got the new generation TB and have the same thing wrong. I know everything is done correctly, but my idle is down to 740 RPM and
shifts are a little lower (5700 compared to 6100)
than before. I wonder if there is a slight miscalculation in the position of the TPS holes.
Anyone who had the original TB will remember that an ATX idled high & shifted funny until the correct holes were drilled. I manually downshift
now; the car used to downshift into 1st up to 28
mph, now it won't over 22 mph unless you move the
shifter. Since the Diablo chip never did raise my shift points to 6500+ RPM, it's O.K. with me.