2008 rancher 420 fueling issues

I just traded my Polaris for a Honda but the rancher seems to have fueling issues, at least I believe. The four wheeler turns on and cranks up but after running for a while it starts to sputter a little. If I put it in gear and go it’ll go for about 100ft and die. The guy said it may need a new ECU. He also said he just replaced the fuel pump. Is the ECU really the problem? I’m really not sure what it could be but I’m thinking it’s got something to do with the fuel injection or something fuel related. I’m really hoping it’s a cheap and easy fix because I got a good deal and he seemed to be a straight forward honest guy. Any help is appreciated. Thank you!!