Not accelerating properly and intermittent not idling issue?

Hey y'all, pray all are well. My truck has a new engine after number 4 piston skirt broke. I still have acceleration issues. When I'm driving and try to give it gas it won't respond unless I press the foot pedal down slowly or press it down fast and release it and it seems to get past the dead spot and runs good. It seems to be worse when cold but not always. Also, when idling it will drop to 500 RPMs and act like it's going to shut off. Every time it happens the bad part? Corrects itself and idles properly. I have bought two TPS and IAC parts but did not fix it. Like right now I am idling, and it is fine then all of the sudden it acts up again. Have new EGR also. It seems to act up a little less when I use the A/C. My mileage has dropped from 15+ mpg to 10-12 mpg or less because of this. As always Thanks so much, BOBBYB