When I switched to a solid cam in my Hemi, I didn't realize I had a repop pushrod & the cam ate it up. I had the same symptoms as you, but living Reno, the August temps were up to 100 degrees & the methanol in the pump gas, made the fuel boil at a much lower temp & bingo, vapor lock. I put the factory vapor separator w/ return line & it solved the problem, but the pushrod was already going south. Put an Eddy mechanical pump w/ 130 lbs of spring pressure & the rod didn't last long. Had to switch to a Holley electric pump & larger return line. No problems since, but I think you should pull the rod out & check the cam end. Find an original OEM pushrod & have its hardness checked. My understanding is that the factory rods were of a harder steel & won't buckle under the pressure & low zinc oils. Best wishes in getting it running.