i have a maroon 98 chevy blazer 4x4 4.3 v6 the engine has 194k miles on it and 50,000 miles ago i had the transmission rebuilt my problem is i was doing about 40-45 mph getting ready to go up hill when i got on the gas some more and all of a sudden i lost power and my rpms shot up until i left off and my take offs are very slow could anybody please help me figure out my problem

 

Have you checked the fuel filter for restriction?
Have you checked fuel pressure and leakdown at the service port AND at the fuel filter outlet?
Has any tune up work been done recently?