I’ve been having almost the same exact problem with my 98 k2500 5.7. Started out as a miss just at idle and slowly got to a very bad miss all the time and spits and sputters when you try to speed up. Just did the MPFI a couple months ago and ran awesome. I just put a new distributor in with no change. Have 58 psi of fuel pressure with engine off and 52 psi with it on. Cleaned the MAF too with no change. No codes at all either. What would be the next thing to check?
Maybe start a new thread? Unfortunately, seems like misfires are not uncommon on these engines and intermittent misfires are challenging to diagnose. It could be many things. A scanner with live data is going to be your best tool (along with some basic diagnosis knowledge) on finding the problem, especially if you don't have any codes. Also, always cover your basics and never trust new parts.
With the information you provided, I'd probably rule out fuel delivery problems, after making sure your fuel pressure is maintained while driving around (under load when the problem happens.)