Still tranny problem

My tranny seems to jump between gears when its not supposed to, when i hit the gas from 0 doesnt matter how hard it jumps right into second goes back into 1st and back to 2nd which causes an annoying knockback. My mechanic told me to go to the dealer and update my computer. I tried manually shifting the gears, there is really no problems then until i put it into OD gear. Any thoughts, suggestions?

This sounds like a computer issue however it could be an internal problem. Take it to a tranny shop and have them scan the computer to see what is happening. On most cars you can disconnect the battery for a period of time and the computer will reset to the stock settings. Most of the cars today have adaptive shifting which means it learns your habits and shifts that way. A diagnosis will give you more information and tell you what to do next. Good Luck!

Any chance of telling us what year this is, what engine??

1998 Buick Regal GS 3.8 SC, just a guess?

Hehe sry about that thought it showed up in my sig... Its a 1998 Regal GS 3.8 series 2 supercharged :)

Didn't you have a junkyard tranny installed? Are you sure the replacement tranny was the HD version of the 4T65E and from a similar year GS? There are minor variances through the model years in valve body operation and specifically the A & B shift solenoids which are controlled by the PCM in regular drive or overdrive.