Not a auto ac tech, but the metering device sounds like the problem. High head usually gives you high back pressure. A restriction will drop your low side pressure and the more refrigerant you add the lower it will go, hence slugging the compressor with liquid, not good. Is the suctions line sweating?
Is the metering device rated for 134A? 36 to 38 degrees to cold, kinda also sounds like improper size condensor. Wish I could help more, just thought I add my 2 cents. Stu Cool.