So, when driving down the hiway pulling load my truck will not down shift out of o.d. I hit the switch and nothing, it just pulls the motor right down. it will eventually shift from o.d. to second gear once my speed has decreased enough or by dropping it down on the shifter. I cleaned the button and it works fine after testing it. Is there a solenoid on the tranny that controls o/d or any other help would be appreciated. Oh yeah, truck is a 1991 W150 w/ 318 TBI.

 

The OD solenoid is inside the tranny. A picture is worth a thousand words.

http://www.scribd.com/doc/228727/Dod...Service-Manual