1998 Chevrolet Silverado bent push rods

Purchased truck from auction, had misfire, found 2- rocker arm studs pulled up from head. Replaced with tapped in threaded studs. Ran great for a few days, then 2- more pulled up so I replaced all with new threaded ones & new nuts. Set tourqe to specs. Ran super, till next morning. When starting noticed clank & backfire. Another pus rod bent. Replaced it set again, ran perfect. Good oil pressure 60 cold 30 hot. Code shows random misfire?Started this AM runs rough for 2-3 minuits then smooth as could be. Has all new electrical parts like, dist. Cap & rotor, plugs, wires,
called former owner said he had intake manifold gasket replaced recently and $ 1200.00 tune up? Sounds like the timing is off when cold sometimes it cranks like that, other times it starts right up and runs fine. Could the TPS be bad?