1996 4x4 Jimmy Transmission Problems

Tranny seems to lack power in 2nd. Happened one day while accelerating onto the interstate, it shifted into 2nd and I punched it to go around grandpa. RPM's escalated with no real increase in speed. Since then (drove home), once it shifts into 2nd there is no power or increase in speed. Also around 55-60 I can feel a little bit of "slip". Fluid level is fine, reverse works, no noticeable noise and no engine trouble light.