Brake pedal travel excessive then will not release has to be pulled back manualy

SOURCE: 1998 chevy s10- brake pedal goes to the floor-

Did you put fresh fluid in the master cylinder? I really think you still have air in the lines. To bleed manually, start with the bleeder the greatest distance from the master cylinder, car running, helper pushing down about half way on brake pedal and releasing 3 times, on 3rd time, holding pedal down to half way depressed point while you open the bleeder valve. Repeat until you are sure all air has been flushed out. Check master cyl reservoir level often, because if it gets low and you **** air into the system, you have to start all over again. Go to wheel next greatest distance from master cyl, repeat above, working your way to wheel closest to master cyl last.

SOURCE: brake pedal goes soft when engin is running on 1998 chevy 1500

If your rubber brake lines are from the factory those hoses can stretch when the brakes are applied. This same thing happened to me. I replaced the master cylinder, with little to no change. So then I changed the brake booster. And if you read the fine print if either the brake booster or the master cylinder go bad it can take the other with it. So if the rubber brake lines don't fix this I would look at replacing both the master cylinder and the brake booster at the same time. But if you would like to trouble shoot this issue a bit more you can clamp off just the rear brakes or just the front brakes or even clamp off 3 of 4 or if it might be a issue before it even hits the brakes them self you can clamp off all 4 of the brakes to see were the problem is. This is to test fewer components at once and to see if the issue is with the cylinders / calipers or hoses. This will help you determine the location of the problem faster and with out throwing parts at your truck and hopping it fixes the issue.

SOURCE: I have excessive brake travel, and a hard time 98 chevy blazer

Two issues...
The brake booster has a ruptured diaphragm. Replace the booster.
It is located under the hood between the brake master cylinder and the firewall.

Your master cylinder may be leaking fluid internally past the plunger.
Have it examined when you change the booster.

SOURCE: Spongy brake pedal even after ABS bleed and base brake bleed.

Did you adjust the rear shoes out? If the rear drum brakes are out of adjustment they will give you a lot of pedal travel. If the pads are worn have no fear of that U-CLIP brake spring, just change one shoe at a time. Take the spring off one side, change the shoe, put the spring back on the post and do the same to the other shoe, no problem.

SOURCE: 1999 Chevy Tahoe- Soft Brake Pedal

Try having the dealer flush and bleed your system. It is very hard to bleed ABS systems yourself and have safe brakes that still work afterward. Bleeding non-ABS brakes yourself is easy not the same for ABS brakes. Valving, sensors and what-not require a tech and the correct equipment in my opinion. You do it wrong and you could ruin your ABS system. Do that and see if they firm up. I replaced my brake shoes/pads at the same time all new everything in back, drums/springs everything and new rotors up front. then I had the chevy dealer flush, refill and bleed system. Stiffer pedal and brakes work better. Keep in mind the brakes on 99 Tahoes are inaedequate, require new rotors often, heat up and fade/glaze pads regularly. I replace my pads long before they wear down because they glaze up and start fading early. I'll rough em up once maybe, next time, new ones. Every two brake jobs, new rotors for me. Just how it is. They will stiffen a bit and work better but they will never be awesome brakes. Just how it is on 99 and earlier Tahoes. Hope it helps. Very important to bleed correctly though. I'll bleed my 83 Toyota 4x4 myself but not the Tahoe.