Can't figure out the problem...
 

2000 F150 5.4L that only acts up when its warm, when its cold it runs fine.

Has no power and acts as if its choking. 140,000 kms. Plugs, COPS, fuel filter and MAF have all been replaced.

(just a warning to those running a drop in K&N filter, the oil on it could potentially get on the MAF sensor and throw the code like it did on mine)

Vacuum lines have been checked as well. When in neutral truck runs and revs as usual, just no power under load.

Truck is throwing zero codes now but still has the problem. I'm thinking potentially cat converters are plugged or fuel pump (I haven't checked the fuel pressure at the rail), any other suggestions?

Without codes popping up I would look toward a fuel delivery problem. Like you said," I haven't checked the fuel pressure at the rail" - do that first.
If you have access to a scanner [not a code reader] watch the front O2 sensors switching to see if they are slow or leaning toward being out of range.