my 4.6 will start and idle, but when in drive, it has no power and it hardly accelerates, the spark plugs are new, and coil packs have recently been replaced. any suggestions?

 

My 4.6 had the same problem. Try this; pull the vacum line off the EGR valve. At an idle aply vacum with a hand pump the engine should run rough. If not the EGR will be cloged. Pull the EGR and the EGR Plenum from the intake. Visually inspect the Plenum it should be completely clogged with carbon clean the carbon from EGR and EGR Plenum ports and replace back on the manifold. This should fix your hesitation and power problem it did so for my 4.6

 

almost forgot when I did this I got a new gasket for my EGR valve.