I changed my brake fluid out on my 2002 Ram 1500 day before yesterday and noticed a firmer pedal, but accompanying that firmer pedal was a hiss I havent noticed before when I pushed the brake pedal. I searched on this and found...........well nothing. Some say its normal, some say air in the lines....whatever. In my opinion it cant be normal if I didnt hear it before and am hearing it now. It doesnt hiss all the time, just during pedal travel. Once the pedal has traveled to where it there is no hiss. It sounds almost like a rush of air. Anyway, yesterday I decided to rebleed the system to rule out the air idea. The hiss is still there, but now the pedal is really hard. Not the typical brake booster is bad hard but way firmer then it used to be. Also it has no problems stopping the truck at all and will lock up the front brakes (rear ABS). I havent checked the vacuum lines to the booster yet but will when the sun comes out. Basically I think my booster is on its way out though, heres why. When I shut the engine off, I have the normal 3 pumps or so of vacuum left before the pedal gets hard. If I shut the truck off and dont pump the pedal, and go back 10 minutes later the pedal is hard already. I think Im losing vacuum (reserve vacuum) somewhere. Also, when I push the pedal in and then start the truck, it does travel normally with little effort. Any ideas on where the problem may lie? If it is the booster, how would bleeding the brakes suddenly cause this problem to manifest? Heres what I did to bleed the brakes and change out the fluid to eliminate any guessing there: With one of those "one man bleeder" kits, store bought not homemade, I started at the right rear tire, then left rear, right front, left front. I drained them all until I saw fresh fluid come out into the container. The bleeder bottle was always kept above the bleeder valve on the calipers, and also had enough brake fluid in the bottom to reach the hose on the inside of the bottle. I pumped the pedal by hand and made sure it didnt travel all the way down. The range was between half to 80% of motion. The reservoir never went below half full as well. Thanks in advance for any help, ideas, criticism or speculation offered.