Broken spring in the valve body per Kennedy Transmission. $180 parts and labor which includes fluid and new filter. check the tps sensor...
It could be a number of things going wrong. Try dropping the transmission pan and changing the transmission oil filter and transmission fluid.
have you checked the oil level in the transmission ? I'm betting the answer is no
THIS IS A COMMON PROBLEM ON THE GM TRANS WHICH IS A BROKEN 1-2 ACCUMULATOR SPRING
no oil in trans
When was the last time you changed your transmission fluid? As the fluid gets older, transmissions start to shift harder, and you notice the shifts from gear to gear a lot more. It could also mean that your transmission needs repair.
pulse generator is bad
I recently had this very problem with my 1996 Buick Century and it was in need of a new transmission and would have cost $1100-$1500 to fix, so I went and bought a Toyota Corolla.
This is called limp mode for that 604 transmission, it means something is wrong internally with the transmission and it needs to go to the repair shop for further diagnosis.
You probably have a slipping clutch band in your transmission. Take it to a transmission shop.
You probley installed the filter wrong. Remove the transmission pan and check the filter.
if it is not going into gear when it is started, if it is a standard transmission then it could be that your clutch is not engaging or that your gears are stripped in the caseing of the transmission, if it is an automatic then your torque converter could be bad or there is something wrong with the shift linkage
Depends on what your transmission is. If it's a manual, it may simply not be broken in quite yet, and you should double clutch, rather than float. It could also be possible that you're hitting the gears wrong.