i need help,,engine trouble

[68GMC454]

ok today i got my dually together fired it up...at first she just purred, sounded great when revved up...then all of a sudden i got a slight knock in the front of the engine....now let me say this,,
all we did was replace all the gaskets and seals except for the head gaskets..but i didnt pull the heads...when i first started it, the intake gasket was leaking, so got it tightened up enough to quit leaking. but when i shut it down, the heatyer hoses and water hoses are darn near hot enough to burn your hand when you touch them...i was told there coupld possibly be a air bubble somewhere in it, and that wouldnt let the water circulate...

is this true...my motor is a 1984 454, 210 horsepower 340 torque..i think thats what the stock numbers for it are...

so what do i do,,need information asap...i appreciate any and all help.

also, i have 6 quarts of oil and a bottle of lucas in it now, and it is still showing low on the dip stick... need all the help i can get..
thanks
billy