You said you thought you may have gotten some bad gas, have you put some fresh gas in yet? Is the carb tight to the manifold, is the manifold tight to the head? I'm sure you could up the timing to 8-10 degrees without hurting anything. Does the truck have power brakes? If so check the line to the booster, sometimes the check valve goes bad it is usually plastic and time and heat are not it's friend. How about the vacum line to the pcv valve , the rubber hose get oily and will be loose fitting on the connection to the intake manifold or the valve itself, and then you have a vacum leak.
Just some thoughts.
