Chuecoman

Hi, I am new to this, but not to car repairs. My C1500 was someone else's problem before I bought it. This truck was running fine, until the weather got cold, now it will not start without a shot of starting fluid. The fuel pressure is low when cranking. At first when I turn the key, it pops up to almost 60psi, then drops to 10psi. During cranking engine, I have about 40psi.
I had the intake plenum off a few weeks ago and replaced the fuel regulator. There was some crap behind the regulator, like small grains of sand. I suppose there could be more I did not remove. Fuel pump is a new Bosch, Filter is also new. Today I blocked off the return line and it had no effect on fuel pressure.
Any ideas? Should I replace the fuel injector set?