1997 K2500 Chevy surging between 45-60 Mph

[John Sampson]

Vortec 5.7L "R" code Engine surges at highway speed after warming up. Engine has very strong acceleration at any speed and idles smoothly. Had to replace intake gasket and a plugged injector. I did a Complete tune-up and performed compression test. Test was good, as all cylinders were between 150 - 200. Service manual says that lowest reading must be no less that 70% of the highest reading. However, I can't get rid of the surge/chuggle. Service manual mentions oxygen sensors and intermitent egr motor problem. Previous owner removed catalytic converters. No trouble codes are stored and service engine light is not illuminated. Will the lack of converters or a lack of exhaust back pressure cause this problem? Egr motor appears to be relatively clean in the port opening. Truck has 170k miles. I don't have a scan tool that will read live data. Any suggestions? Am I going down the wrong path ?

[TweakedGM]

Did your truck do this ever since you bought it.