84 toyota tercel 4x4 trans problem help

I have a Toyota and it runs fine for awhile the trans runs great then after 1/2 or longer it seems not wanting to go into the higher gears I can only drive lows speed when I jump on the gas is doesn't slip it feels like it stayking in low gear.

it this a bad transmisson or does it need an adjustment? the fluid is bright red a shop said put a new filter in it and fluid they said they would do it for 89.00 but wouldn't guarantee it would help

thanks for any advise you have