F150 Rough Idle misfires taking off bad shake at low RPM

I will explain best I can. I am not a shark at this subject. So I lost my dad to cancer in 2016 he gave me a f150 2003 4.2L . It’s very high in my miles over 300thousand but it was running very until now. I was told it has to blown valves in the head. I have tried fixing a lot of things my self like injectors oxygen sensor fuel pump. But can’t seem to locate the problem. It will fire right up but I have to give it gas to make it stay on. I have drove it in this shape but it has rough and tough ride. Shaking and bucking until passed 2rpm then smoothies out a bit idle high at take off not over heating and no oil mix how can I figure out the problem or is time to put my dads truck to rest. Please help I’m having a baby next month and it’s my only transportation.