Gehl RS6-42 wont run

HELP!!!!!! I have a Gehl RS6-42 with a John Deere 4045tf275 enginethat was running and dying and cranked back up but would have low power.This was a new customer at the time and he insisted on changing the injection pump because somebody told him it needed a new one.Anyway, replaced injection pump and unit has not run since.I checked all the electrical and pulled injector nozzles and had tested,Checked and rechecked timing and all checked ok. Condemned and replaced injection pump again, replaced all nozzles and unit still cranks but will not start. Checked compression found one cylinder under 200 psi and one around 50 Psi looked so decided to infram!e unit. Now unit has new liners and pistons,rod and main bearings, reworked head,, new injector nozzles, new transfer pump, new supply and return lines from tank to engine, and still cranks but wont start and run. I have also replaced the ECM and taken to RDO and had programmed. I have had 3 other guys look at it and everybody says " it should crank and run". Have had John Deere service Tech come scan it and go thru it checked and rechecked timing, installed a third injection pump,Pulled front cover to check gear train replaced Injector Nozzles again replaced starteretc. etc. etc. so, Basically everything engine wise is new except the block ,all fuses and electrical seem to check ok but unit still cranks but wont start and run , can get to run on ether but wont pickup fuel and run on its own. ALL iDEAS ARE APPRECIATED , IjUST WANT TO GET THIS THING FINISHED!

Gehl RS6-42 wont run