98 Ranger OD light blinking

My Ranger's OD light comes on blinking every other time I drive. The shift from 1st to 2nd goes hard when this happens. My dealer said that the code wasn't in the manual and they could not make it fail. It seems that it happens more ferquently now. Sometimes when I'm going under 40 and others only when I reach turnpike speed. Any ideas???

i hate to be the bearrer of bad news but my 2000 did that and the valve body gasket blew apart & blocked off the sensors & fluid passages & burnt out the clutches. $1800 to rebuild. same exact symptoms. it's gonna stop workin real soon!!!

Well the dealer finally found out what the trouble was and it turns out to be a bad solenoid for the torque converter. My extended warranty should of covered it but the company Pro-tech is in chapter 11. The cost wasn't to terrible $275.00. Thanks for the input