98 GTP trans shutter

so sometimes when i hit the accelerator and its about to shift from first to second... the trans will shutter and feel like its slipping. Ive got a DHP V1.0 computer hooked up and that boosted the trans pressure and that seemed to help but now its starting to do it again... Whats wrong and how can i fix it?

It would be helpful to post your mileage.

Any SES/CEL light? Some tranny slippage and pressure control related DTCs may be stored even without a SES/CEL light setting. I would get it scanned with a trans capable scanner. When was the last tranny service - ATF and screen filter?

i bought the car at 120000 and its got 136000 now i havent changed the fitler and what not YET. i was planning on buying a shift kit and doing it then but no codes are thrown.

That doesn't sound good. Look at and smell the fluid if it smells burnt than you probably have some internal damage and just putting in a shift kit will only temporarily mask the problem.