Issues with charging system

[scherpich]

So I am having trouble keeping my battery charged, I charge it until my trickle charger says it's good, and after 2 starts with my truck it is struggling again. I've had my alternator (1-wire 90A, brand new) load tested, and the battery independently tested, and both are good. The wiring is a brand-new Painless 18 circuit setup.

Are my grounds faulty? I've relocated my battery to the rear, and grounded the negative terminal to the frame. The motor is also grounded. The battery cable is 2 awg from Home Depot. I also use a Ford-style remote solenoid, which shouldn't really matter.