question?

my truck has been shifting itself out of gear while im driving it and the temperature gauge is jumping i found alot of rust in my radiator and i flushed it out and its still doing it so what else could be wrong im lost

sounds like a termostat hanging shut

and the trans sound like the sycrniser is going out does it grind going in to gears

no it don't grind it just goes in and out of gear while driving it feels like it kicks itself out of overdrive