94 E150 Tranny Problem

302 motor, 130K miles, tranny fluid/filter replaced at 80K. Problem first happened 6 months ago while on a trip, interstate speed of 78mph for 3hrs, came upon a hill and as it kicked in to maintain cruise speed, engine raced and tranny seemed like it was in nuetral. this happened a couple more times on hills only. finished trip at 70mph no problems. had fluid and filter changed again, now 6 months later it started acting up again but now at numerous speeds 35 - 55mph. over the 6 months no real hint of problems. Hoping it is something simple, any thoughts anybody?

The very first thing to check is the ATF level. It MUST be up to, if not slightly over the "full" line when at 60*-120*F on a flat surface with the engine running in "P". If the fluid level is even a little low on this model of trans, yes you can get slipping on hills or during cornering.

I will recheck it