aagh what have I done ??!!

If you shifted with the jakes on. I'm willing to bet that it didn't go all the way into gear and even tho it had pull it skipped and jumped and made a loud bang. That's what it sounds like to me. I've done it once and now I try to never shift with the jakes on lol.

 

Trailer shouldn't be sliding on the fifth wheel...Empty trailer on not.... Might want to adjust Fifth wheel or replace it....

 

First thing I would do is check the engine oil and coolant levels, then turn the motor 720 degrees to be sure it is not an internal problem, then do the tranny and diffs, You should have a spare 3/4 NPT magnetic plug, if you do you own servicing, and do regular plug swaps, keeping them clean and as diagnostics.
Just a thought!

 

Turn the motor by hand via the flywheel or ring gear two full revolutions (360 degrees x 2 = 720 degrees). This way it will go through all possible combinations of moving part positions and you should detect if anything is out of position. If nothing fowls or locks up it is a good indication is nothing is out of place in the motor.If it locks up then you have an issue in the motor.I don't think it is this as you did not mention any issues with the motor running funny after the incident. I tend to think it is probably a gear that was not engaged properly in your gearbox that then jumped a few teeth upon input torque. You may have got away with no evident damage.

 

if you drove it on home apparently it wasn't catastrophic, but how in the heck can ya wait 2 days to find out if something is wrong??

 

you most likely didn't have it in gear all the way when they jump out under a load it sounds pretty bad its most likely ok

 

its simple to figure out if it jumped out of gear. when you continued on did you have to put it back in gear? if so , you were just hifting like a Wildman , didn't have in gear and it popped out, sounds bad when it happens