Spongy Brakes Question

[SS Tim]

Do not continue to drive the truck like this!
If the light is on you are/were seeing a pressure differential between the two sides of the system. Spongy is due to air in the system. If you can't get a good flow at the bleeders its probably the master cylinder. Sounds like the system has not been serviced (or flushed) in a while if you had to drill out a bleeder. Did you carefully check all four wheel cylinders for leakage, including under the cups?
Might just want to pull up the factory manual and do a systems review in chaper 5 on the brakes and the distribution valve/warning lamp functions.