My heat gose from vent to defrost when i accelerate i think its a vacumm leak but no clue where to look

Yes, there is a plastic vacuum supply line the runs from the intake manifold thru the firewall to the heater control panel. Check where that line attaches to the intake manifold. There is usually a stub of regular vacuum hose glued to the plastic line that can crack and leak at the manifold. If it's ok there, trace it into the truck. There may be a tee somewhere that is leaking inside, or else the connection at the mode switch or possibly the switch itself. Take the control panel out (you may have to pull the bezel off to expose the screws) and listen to the switch with the engine running. Try tugging on the lines to see if the leak gets worse. Worse case, you will need a new switch, but try to rule out any tees or hoses first. OK?