No start unless starting fluid added 96 Yukon csfi.

I started having this problem a while back. When I first bought the truck less than a year ago, It will start with a tap of the key, then it would start after cranking it 3 times, then about ten , now no start unless I add starting fluid. It'll start the first time I crank it and run fine afterwards, if I let it sit for a few minutes it won't start again. It used to be I had to let it sit over night. I checked fuel pressure key on engine off, it was about 50 - 55 psi, running went up about 2-3 psi. Engine off, pump not running went from 55 psi to 35 psi within 3 minutes . Don't know if it has a check valve on the return side that's not holding pressure or if it's leaking back through the pressure side or if its a leaking injector or regulator. I'll check the return side by pinching the line and the regulator by taking of the vaccuum hose. But if that's not it How can I check the rest. I know the pressure is low to start off with so I'll change the filter but I'm pretty sure it's not causing the fuel to leak back. The truck also has 278k + miles so it could be anything. Any suggestions would be helpful. I don't want to start throwing parts at the truck I'm gonna end up putting different engine in it and might have to change the parts again.

Found out the problem. I pinched the pressure line and kept an eye at the gauge. pressure went down slowly, but as soon as took off the clamp pressure dropped from 45psi to 20 psi. Changed the fuel pump and pulsator. Seemed to do the trick.

278K on a 96? Do you drive cross country? That's great!