replaced brake system on 97 1500 brakes still mushy dash light on now

pushrod length too long ? bent shake brace.Firewall flex or broken welds. debris trapped between master cyl. piston and snap ring, incorrect part usage. Internal p[rblems in contol valving your system uses. Get it to a brake specialist or your GM dealer because you need some experienced minds viewing and judging the results of the tests performed. having contaminated fluid can be enough by itself to cause much of this. Discuss thoroughly with service manager and ask for tests and diagnosis rather than a list of operations performed that fix it by dumb luck.

Did you properly bleed all the air out. Sounds like you still have some trapped in the system. Also brake calipers locking up is typically caused by the rubber hose going to them being internally collapsed. This tends to happen shortly after brake calipers have been replaced due to the hoses having been moved around a lot during the caliper change.

To add to dandyoun's info, letting the calipers weight hang on the hoses can stretch and tear them internally if they have had time to age, or have been enduring stretching from being pulled upon. That is the logical explanation if you were to damage both and have the symptom appear at both at the same time.

Fluid contamination can also explain why both were staying applied. The internal softening of the hose liner can lead to obstruction after handling improperly during a brake job. The tests would include inspection for geyser after warm at the offending wheel(s). Then remove the hose and attempt to pass shop air thru in both directions. That is, of course, if you had the symptoms lead there, and your vehicle passed all the inspections mentioned previously. You know your vehicle and your circumstances better than anyone , so if these conditions were present, you can decide for yourself. Since the bleeding is crucial to a safe system, I still recommend a brake shop, or the dealer for the bleed tool.