1990 Chevrolet Truck Started Chevy K1500 Just Fine This Morning Began Pull Off

I started my 1990 Chevy K1500 just fine this morning but when I began to pull off the accelerator felt stuck. I pressed a little harder and it worked normally but took a long rev before sounding like it was going into gear. Once I was on my way it was fine but after cresting a hill and hitting stop and go traffic the problem persisted-the long rev then a sharp gear change.
In the past 6 months I have replaced my fuel pump, distributor (and cap), transmission, coolant hoses, battery and header gaskets and really have no idea what else to do. I work 88 round trip miles a day from home and need my vehicle to survive please help!