For awhile now, my car has slightly hesitated to shift into overdrive. When it was supposed to shift into overdrive (under medium-light acceleration) the rpms would spike and it would take several seconds to shift. Well today, it stopped shifting into 3rd and overdrive altogether. 2nd is really mushy too, if I try to accelerate it will jerk forward like it's trying to grab but can't. I have checked the fluid and the fluid is not brown or a burnt color, it's still red. The fluid did not really smell all that burnt either. The fluid is also at the proper level. What could this be? Torque converter?

I drive a 98 Pontiac Trans Am with the 4L60E. Car has 75,000 original miles.

All help appreciated! Thanks!