Dodge RAM 1500 3.7L V6

if it has been sitting for a few years, the gas is bad and you should not even start the truck- gummy gas throughout your fuel system now- it doesn't matter if your son "decided to rev" the engine or not- there are many issues that will need to be resolved since that thing was most likely put away wet- I think a good garage/mechanic is next on the agenda-

What would I be looking at cost wise new fuel injectors etc

Potentially a good bit. The worst case scenario could mean a new fuel pump, clean out the fuel lines and gas tank , new filter and new injectors.

I already replaced the fuel pump and cleaned the gas tank I was thinking of using fuel injector cleaner with 91 gas to see where I stand after I'll replace the injectors and lines

Can't go wrong with Seafoam additive in the fuel tank. It cleans the gummy residue out fast.