If it went to full throttle and would not come back down when moving the throttle sound like the classic case of gears stripped in the injection pump, but I didn't think this age (05) tractors were suspect. Most of those were late 06 -to early 08 vintage. Don't panic right now, do a few tests.
1. Is the fuel filter bowl full of fuel? If not blow back through line to tank and see if it flows better. Then bleed the filter.
2. Follow the fuel line from filter to the Injection pump and take that line loose and crank the engine to see if there is good flow of fuel there. If not, fuel filter is plugged or lift pump not working. If this is OK try next test.
3. use 17mm wrench to loosen 1 or 2 of the nuts on injection lines at the injectors (about 1/2 - 1 full tur)n of nut), crank engine to see if fuel is flowing. If no fuel present remove the fuel stop solenoid from the injection pump and try cranking again. If there is fuel now, the stop solenoid is stuck. If still no fuel to the injectors the pump gears are very likely stripped.
Hopefully RicheyVS will come on here. He is quite well versed in these pumps and can give some better insight in testing/inspection of movement of the fuel rack.
