Quits going up hill

I have an 06 Recon TRX250ES and when I start up a hill that is somewhat steep if I let off the gas to down shift or anything that requires letting off the gas it will die. It starts back but it just dies. but when I am setting on level or less of a slope then the engine will idle. I have started running 89 from a better supplier and it has helped in other areas but it still dies on steeper hills.