Chevrolet Repair: 95 Blazer RPM Surges at Highway speed, tank fuel, highway speed

Question
Hi,
I have a 95 Blazer with a vin Z CPI engine that has sat in a garage for a year.  I recently did a tune up including new plugs, wires, cap, rotor, and ignition coil.  I have also replaced the gas tank, fuel pump and sending unit.

The truck seems to run fine at idle and just cruising around town, but when i get on the highway running ~100km/h the engine has constant slight 50-100 RPM surges when trying to maintain speed.  If I give it more gas the problem will stop until I level out the speed then it starts again.

All the other problems I searched relating to this issue seemed to have other issues like poor idle etc.  My blazer idles perfectly, accelerates well, and the Engine light is NOT on.

Any suggestion on where to start troubleshooting?

Answer
Hi Dallas, seeing as it sat for a year i would suspect that you have a fuel inj problem... try a good inj cleaner. also you don't say if you replaced the fuel filter. if not i would. old fuel will clog up inj. and filter... try that and see it looks like you have covered everthing else.  hope this helps