hpop or leak???? help
so a mth ago my truck left me on side the road. towed to the shop and was told I needed a hpop and had a leaking hg. so I decided to go ahead a bulletproof it. had it studded, stc fitting, dummy plug, stand pipe, oil cooler, coolant filter, blue spring, sure im missing a few little things. welllllllll someone had a wrecked f250 and sold me the hpop for $200. I bought the pump trying to save some $$$ bc in the mix I had 2 scared cylinders that were unexpected. after the truck was in the shop for 2 weeks I picked up on a Friday. well Saturday am truck started fine and rode abt an hr or better came home parked it. 30 min go by I go to leave the house and crank but no start. guy from the shop came look at it(took about an hr to get here) and it starts right up. he hooks his laptop with the dig program and no codes come up. he let the truck run for awhile to get hot and then kills it. crank no start. The hpop pressure would only get up to around 320psi. gave it a shot of ether and started up. his computer showed desired psi then actually psi. when running and hot it stays within the desired pressure but jumps around a lot but stays within 20psi of the desired pressure. now he saying I need a new hpop (only thing not under warranty bc I bought used). I was told if the truck runs then the pump is good and if the pump was bad it wouldn't start at all??? so do I have a leak and he isn't owning up to it? sorry for the long story but wanted to give as much info as I could.