I have the same problem on my 05 4.0 ranger. Surges for about 1.5-2 seconds then fine... Talked to the mechanic he said I just need new spark plugs and wire and that would stop it. But he said that the surge is nothing to worry about....
2005 4.0 FX4
Tinted out (15% front, 1% back glass and quarters, 5% winshield strip), Line X Bedliner, Flowmaster Super 40, T-Bar Crank with 265 Firestone AT's
Memphis Power Reference 10 in a ported box, 400 watt amp, 8000k 55w HID's
Mods to come...