Shifting Problem

On occasion my 2001 Monte Carlo SS will sometimes upshift all the way to 4th gear when leaving a stop sign. Then it will lug & vibrate obviously from being in high gear at a low speed. I can pull over & shut car off for a minute then start it again & it will shift just fine like normal. Then randomly out of the blue it will do it again without any sort of pattern. I replaced the main computer but that didnt help. Can someone help me please?

You need a full scan with a trans specialty scanner, then a proper diagnosis can be done, this process allows the tech to check solenoid functions and command up/downshifts.