As for fluid movement in the master cylinder, this is normal. With the cap off it will spray out everywhere.
My service manual doesn't mention anything about a flashing brake light, just on continuously or inoperative. The only thing I think that is supposed to make it flash is if the jumper wire is installed and it is flashing the codes (or is the for the abs light?) When does it flash? Does it come on when the truck is started and then go off after 3 seconds (bulb test) or so? If you don't touch the pedal does it flash on it's own or will it stay off until you hit the pedal or something? Is it flashing regularly or or just intermittently? On mine I could just tap the brake pedal and the light would go out.
How did you spread the calipers to make room for the new shoes? I've read that in the chevy's you should open the bleeder valve and let the pressure out there when pushing the calipers open, supposedly the backwards pressure can damage the abs. But I've never done that in any of my other vehicles.
What are the and such?
Are you sure it's not just still air in the system? How does the pedal feel? How is the braking power?
There are several things that are supposed to make the brake light come on.
Since yours isn't inop, I will write the on continuously brake warning system diagnosis routine. Mine wasn't really on continuously either, just came on when the pedal was pushed. Not exactly the fail you are getting, but may give you some info of where else to check for problems.
Step1: Disconnect park brake switch connector (left floor board above the parking brake pedal). Turn ignition to run. Check that the parking brake is released. In my case I also performed whatever it was that made the light come on (pushed pedal nearly to the floor).
Result1: Light turns off.
Action 1: Check for adjustment of parking brake switch or replace if adjustment is ok.
Result 2: Light stays on.
Action 2: Go to step 2.
Step2: Disconnect brake pressure warning switch connector (2 wire connector on rear of EBCM).
Result 1: Light turns off.
Action 1: Diagnose brake system (this was my fail and it was due to air, still).
Result 2: Light stays on.
Action 2: Go to step 3.
Step 3: Disconnect EBCM connector c1 (the big rectangular one with 7-8 wires in it).
Result 1: Light turns off.
Action 1: Diagnose ABS.
Result 2: Light stays on.
Action 2: Go to step 4.
Step 4: Disconnect daytime running lights module connector (buried inside dash to the left of the steering column in front of the cross bar).
Result 1: Light turns off.
Action 1: Go to step 5.
Result 2: Light stays on.
Action 2: Locate and repair tan/wht wire (33) for short to ground between DRL module and instrument cluster.
Step 5: Turn ignition to off. Connect self powered test light from the cavity A of the drl module to ground.
Result 1: Test lamp lights.
Action 1: Locate and repair the lt blu (1134) wire for a short to ground between the drl module and the park brake warning switch.
Result 2: Test lamp does not light.
Action 2: Go to step 6.
Step 6: Connect self powered test light from the cavity F of DRL module to ground.
Result 1: Test lamp lights.
Action 1: Locate and repair the tan/wht wire (33) for a short to ground between the DRL module and diode 1 or the PPL (680) wire for short to ground between diode 1 and the ECBM or brake pressure warning switch.
Result 2: Test lamp does not light.
Action 2: Locate and repair the lt blu wire (1134) for short to ground between the ignition switch and the DRL module. If not short is found, replace the ignition switch.