2001 gtx di will not run at full throttle

[ggoodwin]

i have a 2001 gtx di and we just had a new motor put in it this winter. we took it out two weeks ago and it ran great no problems. A few days ago i took it out ran fine until i gave it full throttle then it would slow down to low rpms and act like it is in limp mode. once you take the key off and restart it, it will run fine until it has full throttle then it goes in to limp mode...............Does anyone know what causes this

also the maitnence light flashes when you give it full throttle
Thanksthrottle