wont rev past 4 grand and black smoke

[mattpresley]

Maybe run seafoam through?

 

[Ranger5.0]

seafoam? Its a new engine. So, I took a closer look at the fuel supply system, still ok. Holds good pressure when under load. Timing is set @ 12oBTDC. Its always ran fine there. I even set it back to 10 and it made no difference. Checked to make sure the ecm is controling the timing and its working properly. It still wont rev' past about 4500rpm. It will some times climp to 5g and then bog down to 4500. As soon as i let off the throttle it starts runing fine. This is really becoming annoying. Anyone dealt with somthing like this befor?