98 Camaro shifting with high RPMs
 

I have a 1998 Camaro with the V6 and automatic transmission. When I shift into drive it kinda jumps. When I get up to about 3500 RPM the car will shift from 1st to 2nd and same from 2nd to 3rd. The service engine soon light is on. The throttle position sensor low voltage is the code it shows. I've changed the sensor and I still have the problem. Anybody else had a problem like this or know what could cause this?