Have a 2003 XLT 4.6L Expedition (160,000mi) that has been awesome, but recently began loosing power at speeds over 45mph (rpms >3000) when towing boat up hill in GA (overdrive off). Runs & shifts smooth w/ no miss fires. Large EGR vacuum line blows off when I floor the gas, but no codes to go by. Researched most forums and can't find answers. I hope you can help.

Here are my readings at idle (and with ACTRON scanner):
EGR line pressure ~ 2PSI (this seems normal back pressure at idle)
idle vacuum test 19psi, increases with higher rpms (no vacuum leaks).
Oxygen Bank 1: 02S11 0.4V, 02S12 0.8V
Oxygen Bank 2: 02S21 0.3V, 02S22 0.7
MAF flow 4.6, Coolant temp: 179 F,
FUEL system 1 closed loop: ST FTRM 3.9%, LTFTRM 7.8%

I ordered an ELMSCAN 5 OBD reader to test engine more before replacing catalytic converters.

Q1) I suspected catalytic converter after it gets hot but how do I test it, what should I look for? When cool the back pressure appears normal.

Q2) How do I find out factory specs on oxygen sensors? they seem ok.

Q3) Does the 2003 Expy have baby cat-convertors or normal ones? I heard baby cats send different signals to computer than normal ones (can't find factory specs).