Smack it harder. If all the bolts are out that should be all it takes. I've had to hit pans pretty hard with a mallet to knock them loose.
1975 Chevy K20 8400lb GVW Camper Special
1971 Gladiator J2000 Platform-Stake Dump 350/T18
1970 Gladiator J3000 3407Z Camper Truck 350/T18
1963 Gladiator J300 Townside 350/TH400