Toyota Repair: 1985 TOYOTA VAN WAGON LE 2.0L

Question
My 1985 TOYOTA VAN WAGON LE 2.0L automatic trans has this problem:
Sometimes cold or hot the trans stucks in first , sometimes stucks in second, never stucks in 3rd.
I play and play with the shifter and after many times it upshifts to second , after playing with the shifter it goes to 3rd.
Is this shift problem caused absolutely by the VALVE BODY or there may be other parts that cause this shift problem inside the trans? (oil level ok)But driving downhill,it shifts automatically, only on  the level road or uphill it hard hard, very hard shifts.
Appreciate your opinion , thanks Fer

Answer
Considering the age of the van it could be the valve body or an internal transmission proble, there is a kick down cable that connects to the throttle body right next to the accelerator cable connection, the shift kickdown cable has a threaded sleeve where the cable comes out with two 14mm nuts, loosen the nuts and adjust the sleeve so the cable sticking out is longer by about 1/8" then give if the shifting improves