we are having troubles with a slight bucking or hesitation when going up any kind of hill, has has all new fuel tank lines pump and filter new spark plugs and wires tranny rebuilt. I was leaning towards maybe a bad injector?

 

Sound like you are losing spark with high demand, a good possibility would be the ignition coil is breaking down with increased load on the ign system. Is it safe to assume the plug gap was checked before installing the new plugs? What you are experiencing is a general loss from the entire engine and 1 injector would give some loss but not as much as what you are describing.

 

Do you happen to have the check engine light on ?