71 k10 lunging? when driving please help

[ooimpalaoo]

ok so once again im calling on your help. my k10 was running great then one day im going to use the word lunged forward. i only use it 3 days a week on the highway and last week it got to the point where it did it like 6 times on the way to work. now my truck is stuck at work i cant move it 20 feet without it doing the same thing. the motor runs great. starts great idles great. revs great. what the hell is going on? any ideas where i should start? thanx for the help