I currently own a 2003 pontiac bonneville a little over 220000. I bought it used back in early 2017 and its worked great up until about a month ago, one of the smoothest cars I've driven. But now When I start the car for the first few miles everything is fine, shifts smoothly, starts in 1st(can't seem to get up to 4th tho, about 2000-2200 rpm at 55 mph) . But then as far as me and my dad can figure out it will get stuck in 2nd gear. I've had it slip out on the highway, my rpms will suddenly drop and then shoot up to 3000 rpm at 50 mph, or (because I've started taking back roads) from a stop light it will not shift into 3rd and then I'm stuck in 2nd(2000 rpm at 35-40ish 3000rpm at 50) for the rest of my drive. Please note after it misses this gear shift and gets stuck, it will start from 0 mph in 2nd gear,cruise control no longer works and my manual gears (1,2,3) dont work except for 2. Check engine light is on constantly. Please if anyone knows the cause to this problem It would be greatly appreciated. One shop said I needed a complete transmission rebuild, have plans to take it in to another shop on monday for they're diagnosed. Can't really afford an entire tranny rebuild, any help would be amazing. Thank you

How'* the fluid? Full? Burnt?

Ever done a transmission service on it?

What codes are stored in the computer?

Did the shop say what was wrong specifically?

Please have the codes scanned, and post them here, including the specific code number.

It sounds like it may be going in to limp mode for some reason, which, if it'* true, would cause the car to hang in 2nd.

I thought it was 3rd gear limp mode?

Check all fuses in engine bay and under dash. There is a fuse that provides power to all the solenoids in the trans. If the fuse is blown, you will only get 3rd gear.

Limp mode is when both shift solenoids and OFF and depends on the trans. Knowing the fault codes is a place to start. Fluid condition is another. Does it smell like burned clutches, hot brakes, or is it just varnished would give an indication of the condition of the clutches. It is possible that it may be a shift solenoid that fails when it gets hot. More information is needed to go any further at this time. Given the mileage a unit replacement might be something to consider if you plan to keep the car for a while. I believe Gm has a $200 rebate and 3yr/100k warranty on their SRTA'*. Get your numbers and and see what works for you either repair or replacement. Again first know the codes and make sure its internal to the trans. Then proceed with how to repair. I know this isn't much help but it'* all I have at this time. Be safe out there.

1.Check fluid level/condition...
2, Check for codes and write them down....
3. A good tech takes a test drive, and a snap shot with a Tech II scan tool, to see if the solenoids are being commanded and if they are creating the proper shift ratios, and if there is any slippage......

A similar thing happened with my 97 Bonneville. It wouldn't shift past second. I scanned it and it had a code for my throttle position sensor. Quick fix. Hope you get that lucky.