2003 STX-12F,With about 30 hours.When I let off the throttle completly after any Substantial amount of RPM's,it will stall.Now if I feather the throttle and let it down slowly it will idle fine.If I rev up the motor most of the time after it revs down it will get to the point where it will almost stall,sometimes it just stalls.I also noticed that when on the trailer it will slightly rev up and down.I am asking for some help to see if anybody has had similiar issues,and their fix.The only things I could think are wrong: 1) TPS(Throttle position sensor)I remember the same problems we had on the older Fords pre OBD II. 2) Bad gas,I was forced to use a no name brand,then it started doing it,and 3) something with the plugs.I just got back not to long ago,so I have not checked anything,buy any help would be appreciated,thank you...