f150v8triton

Hello. 2000 F150 5.4 V8 Triton 106k
Purchased used. 2 weeks ago started misfiring. Check eng light on. Changed coil packs (accel) since they looked original and i wanted to tune it up for the winter. Cleaned MAF. I guess computer cleared up bcus it ran fine. However when i loaded truck up with cargo for a haul, it began to misfire again. Especially when OD kicked in. Completed my trip with OD off and under 40mph. Next changed plugs. It had Autolites. Replaced with motorcraft, gapped to .53 (emission label .52-.56) took my time to clean and vacuum. This time i used dielectric on coil packs. Cleaned tips before installing. I also cleaned K&N air filter and oiled I changed fuel filter as well. Started up and no bueno. Still has a slight miss and with air cond on idle stumbles.. No check eng light. Not sure what to test next. TPS? EGR? EGR CTL Module?FUEL INJECTORS? FUEL PUMP? Clean Throttle body?
Id like to get this solved since i have brake pads and gear oil to change! Thanks.