Truck surges going uphill

I have a 97 k1500 with vortex 350 4l60e that had the fuel pump replaced about a year ago. It runs fine around town but surges when accelerating out of town when cold and when climbing hills. It seems more to happen in overdrive but it can happen in third. Sometimes it does it as low as 1500-1800rpm 45mph and as high as 2000 at 68mph. My wife has commented that it's down this before and gotten progressively worse. When it surges I will press on the accelerator and it sometimes goes away and the rpm goes up. Had my mechanic check it out and couldn't find a problem. He said the spark plugs and wires were fine. However, he did comment one of my cylinders was miss firing. I've ran sea foam and other injector cleaners thru it. Which has only helped the idling.

Thanks for your help.