Ranger "stuck" after being parked

hi all. I have a 98 ranger, 4cyl. manual transmission (2.3L, 2.5? Whatever the smallest is) 2 wd. Anyway, after being parked for awhile, like after work, or when i wake up in the morning-turn the car on, but it in reverse (havent tried 1st yet) and it seems to be fighting itself, as if the parking brake were on. I put the truck in neutral, try to push it, doesn't budge. If i give it quite a bit of gas, it (struggles) then makes kinda a pop/bang noise (not from the exhaust, but something releasing) and im fine. I can turn it off, wait 30min, its fine. Only after sitting for a bit. The truck definitly is trying to move when its "stuck" it rocks when i give it gas etc. It feels just like the parking brake is on, thats the best way i can describe it. i dont think it is on, however, because after that initial pop, its fine, and the break works fine next time i park it. Any ideas??? Thanks alot guys!