My car is 2003 pontiac Montana and recently when I start to drive it, it seems the transmission failed to shift, when I steped on the gas pedal the engine rpm goes high but the car doesn't accelerate

. Check the transmission fluid level. Is it pink or brown? Does it have a burnt smell?

. Check for codes.

. Try dropping and cleaning the transmission pan and magnet, changing the filter, and changing the fluid, if it has not been done in 30,000 miles. If the problem persists, one or more clutch packs may be shot.