ok everyone, i got it all fixed. i wanted to report back in case this helps everyone.
Background is all above... this weekend i did the following:
1. replaced lift pump. no improvement.
2. replace EVERY crush washer on every line. no improvement.
3. pressurized tank. no improvement.
4. Bypassed everything with new 1/2" ID line from tank directly to inlet side of primer pump. tried to prime sytstem... noticed immediately a difference in what priming felt like. you could feel and hear fuel moving. there was resistance on the primer. before, my primer would simply move up and down with ouly the spring resistance. when icracked bleed screw i pumped like less than 10 times and fuel was POURING out of the filter.
5. started mog and it runs perfectly. never had this throttle response etc. i always just figured it was a dog because of it's weight, but it's much more responsive, top speed is higher, etc.
6. i began to plumb back in everything i bypassed, meaning the fuel shutoff valve, and the debris screen. i removed them both, and cut the lines off the brass barbs on each end. I immediately noticed that the barb on the EXIT side of the fuel cutoff was PACKED with debris. which is extremely weird, because i ran 60 psi air through it without any resistance that i noticed. the amount of trash that was packed on the exit side of the valve was insane. it was BEFORE the sediment filter.
all in all, she's running great and has new fuel line on the input side. wasted money on a lift pump.. if anyone needs one, i have a factory unit with new primer i'll sell pretty cheap
it has less than 20 hours on it and i took it apart and everything is pristine condition.
after i got it running, i took of the leaking boom cylinder and it's being repacked as we speak. next up fixing an air leak and finding my coolant leak!
thanks everyone!