Ok, did a little looking this afternoon. I put the truck up on jackstands to get all 4 tires off the ground. Cranked the truck put it in drive, and let the rear tires just spin at idle. Thin I stopped them, put the transmission in N and switched the transfer case into 4HI, and shifted back into drive. Rear tires spin, front driveshaft spins (so transfer case deffinately works), and drivers side front axle spins (open dif), but no front tire movement.
Went ahead and shifted back to 2wd, and killed the truck. With the truck dead, and vacuum hoses removed from IWE, tire still spins freely (like it still has vacuum on it). Put my pump on each IWE, and they both hold about 22#'s. pulled both checks, 1 is bad, will replace both. Hooked 1 side back to the IWE and my pump to the other and cranked the truck. I'm reading on my pump between 20-23#'s on each side.
So where can I find these check valves? And what in the world is up with my stuff!?! Seems like everything is working but the IWE's. And what can spray into the lines to flush them, in case there is some debris in the lines. I'd hate to contaminate the new ones I'll be installing.