2003 Gmc Sierra 1500 Brake issues, bleeding

Allen brake fluid is hydrostatic. That means it attracts moisture just sitting in the master cylinder and the moisture causes the lines to rust from the inside out. Now as long as you drive the truck everyday you won't have a moisture problem. On the other hand if the truck sits for a for a long time or if you use the truck to launch a boat (fresh or salt water makes no difference) those are additional reasons for why the lines rusted and you had to replace them. The problem is you just replaced the lines. Even though you bypassed the ABS module the rust and moisture that already got into the system had enough time to do its damage. That damage is to the check valve in the ABS module and that's why you're not getting any fluid to the front brakes. You can't just replace the check valve. Sorry to be the one to tell you this but you must replace the entire ABS module.

Allens,

Obviously, since we can't see your truck, we don't know exactly how you altered it. Maybe you can explain in detail, how you bypassed the ABS.

Have you gone back to basics and tried bleeding the line at the master cylinder and then at the combo valve, to see if your problem is upstream or downstream? It could be that the master is not bled properly or a problem at the combo. If your getting good pressure from them there must be a restriction downstream. Process of elimination.

Al,

In addition to the basics mentioned by drivability, you can't dismiss what Pete is sayin either. On the other hand and before we apply what Pete is sayin, why don't you tell us:

How you bypassed the ABS module?
How you bypassed it without getting air in it?