The transmission is controlled by the computer and it expects a certain "rev rate" that your mods have obviously gone beyond. So, the truck hits the rev limiter before it can make the shift.

Talk to the person who did your chip and have them adjust both the shifting and the rev limit.

The stock Lightning trannies are about as tough as they come from the factory, but as with everything there are limits, especially when you start playing with sticky tires and torque converters (much more driveline shock).

Later!
Jeff S.
Lightning #74 in '95 - 11.92@115.2
Lightning #582 in '00 - 13.36@101.75