I just bought this 99 firebird formula with only 74k miles on it and the transmission seems to be slipping 2nd and 4th. I bought it in nc and drove it 3 hours back to ga and she drove beautifully. Didnt do anything crazy on the road but suddenly I couldn’t push past 70 mph without the car damn near redlining. One I hit the exit I couldn’t pick up anything past 30 mph. I am not a car person at all and I have no idea what the process is for even diagnosing a tranny issue let alone fixing it. Any guidance would help

 

2nd and 4th gear applied by the band. There may be a servo leak, or your band may be worn out, or both.

Why that would be happening on a unit with such low mileage is the real question.

 

I have seen with cars and trans that sit for a long time in a humid area, The rev drum show signs of rust and the band be delaminated . I mention this because a 99 wih 74k miles means it sat alot or a long time

 

We might be able to help you more if we know what the servo end play is. The servo is covered with a half-dome cap.
Press on the servo cap with a crowbar and hold a ruler nearby to estimate how much it moves in.
1/16" to 1/8" is a good amount. 3/16" is marginal and anything over 1/4" is going to cause the band to start slipping.
You might be able to get a bit more life out of it by buying a longer servo pin or welding a blob at the end of the existing one.
Removing the entire servo does not require removing the trans, although on a Firebird the frame will get in the way; you may have to remove the drive shaft and rear trans mount to tilt the trans down enough to remove the servo.