I noticed lately that my 2002 F150 super crew automatic makes a thump when shifting at around 50 mph or higher. I think also when engaging the passing gear. What can this be?

Also, when going uphill, the A/C changes from vent to defrost on top of instrument panel then back when not under heavy load. I know its a vacuum issue but what exactly and why? Or is this normal?

I don't know if its me but I think my truck feels weak for having a 5.4 in it. All else is working fine as far as I can tell.

 

I would check the tranny mount for the thumping noise.
You have a broken vacuum line. It is probably on the firewall near or behind the battery the goes into the fenderwell to the vacuum canister.