no reverse and the o/d light is blinking

I have been told it could be a speed sensor a throttle body sensor or a speed sensor Or possibly a selinoid any thoughts I just got the truck also the fluid level looks to be over filled

Do this test exactly as i tell you! While driving with trans. in drive and going about 15 mph and NO pedals applied, manually pull the shifter into low gear. Does the truck slow down on it's own or just freewheel? If it has NO engine braking, doesn't go into low gear and slow the truck down then read my first answer again!!! Post the test results for more info.

Ok it down shifts though all the gears fine and the over drive light is not blinking now is this a good thing

Not intrested about any gear but manual low from drive at 15 mph! Do not down shift through the gears, just shift it from drive straight into low to see if the truck slows down!!! That's it. You should let a mechanic test drive the vehicle. Also a scan test will show if it is a electrical solenoid, i don't think so!! Google this problem, it might be something on youtube. I hope i am wrong about your problem. It wont be the first time! Good luck with it.

Thank you!