Check your fluid. Look at the color of it. If it's a bright-ish red, it's good. Brown (or worst case scenario, black) change it. If it doesn't help, you could be looking at a new tranny. Those trannys are reletivley cheap (When based next to other trannys) at about 300 bucks for a used one. The labor on the other hand, will cost a lot more. So, start with the basics, check the fluid. The dipstick SHOULD be near the back on the left side of the intake plenum. You'll see it, it'll be red. (A lot of people think I'm talking about engine oil when I tell them to check the level, so this is why I say it).
1999 Chevrolet Camaro SS (PC'd)
1994 Chevrolet Beretta Z26 Q4 (W41 M90'd)
2004 Chevrolet Silverado 2500 (4WD)
My wife's cars:
1971 Dodge Charger SE (stock and original 383 auto)
2004 Subaru Impreza WRX (kid-hauler)