Loss of power

[xgrizx]

2000 7.3 Excursion. 287 thousand miles. Sat for a year. Changed oil and fuel filter. Put in fuel stabilizer with 5 fresh gallons of fuel. Now shows just under 1/2 tank. Starts fine. No CEL. No smoke. Idles fine. When I drive it won't go over 1600 RPM's. Very slowly will increase speed. Too slow to make it worth talking about. At idle in park RPM"s will increase as normal up to red line. I'm very ignorant to all the different sensors, etc. If it is a known problem please indicate the name of the sensor or valve if that is causing the problem. One fellow said it was the Accelerator Pedal and Sensor Assembly. Another said if that was the problem I would not be able to accelerate at all. With that I don't feel comfortable investing $317.00 for that part. Thanks for any help or advise.