Craftsman LT1500 valve lash goes out of spec when blades engage

Every time I engage the blades on my Craftsman LT1500, the valve lash goes out of spec (loosens) and I get popping sounds. I adjust the engine to TDC, and re spec the lash, and tighten the lock screws down good. This happens within a minute of engaging the blades but no issues when not under load. Spindles seem to be fine and move freely. Intake and Exhaust rods don't seem to be bent either. I do have an aftermarket carb on there, could that be causing the issue? What else could be causing this and how could I diagnose/fix?
 
Craftsman Model # 247.288810
Briggs and Stratton Model 31c707 Type 3346 G2

How could I tell if the Rocker Arm Studs are stripped? I'm assuming the stripping you'd be referring to would be where the lock nut screw screws in to hold the adjustment bolt for the rocker in place, right? I don't believe Part #830 is loose where it connects to the head. I tried to tighten it and it didn't move at all. 
 
I feel like this all started last year when I raised my mower deck up. I had to manually make holes to raise the deck high enough to cut my grass to 3.5". Even on the highest setting after adjusting per the manual, Id get maybe 2.5" which was too short.  Once I got it running at the 3.5", everything was working fine for about 15 mins (with blades engaged) before the valve lash issue came about. After tightening the valve lash back up, I tried testing engaging the blades at the lowest setting and it will still throw the valves off. I feel like this is completely unrelated but worth mentioning incase.