locked up 80 GMC 6 auto

[marvxyz1]

I replaced my gas gauge a couple of weeks ago, and went to take my 80 GMC for a ride. Truck wouldn't budge. Ended up replacing two rear wheel cylinders and disconnected the right emergency brake. The right emergency brake was dragging.. I also noticed that my old wheel cylinders were full of rust inside. Went to move the truck and it still wouldn't budge. In then put the rear wheels up in the air on jack stands, and started er up. The wheels turned freely in both forward and reverse gears. but when I lowered the truck to the ground, something is holding the truck from moving. What the heck is going on??
Could my front wheels be locked up also?? Any input you have on this would be appreciated Thanks marvxyz