Chevy Cheyenne 6.2 bad running
 

Can anyone help with a intermittent fought running and power surge.
I have an ex army Chevy Cheyenne 6.2 cc20903 with only 48000 miles this is a December 1992 model with a 165 hp engine.
I have issues when a low rev's the engine gets lumpy and seems to run on about 4/5 cylinders, but just before this happens I seem to have a power surge from the engine and pulls harder without any further movement on the throttle. Sometimes the engine cuts out, then starts up then ok for a while.
The fuel tank and sock have been clean out, a new fuel filter been fitted and have increased the fuel pump , but this has made no differently at all