When I drive truck at around 35 with O/D off it goes up to 1800-1900 before it wants to upshift. I noticed that if I quickly let go of the gas and then press it again it will upshift and rpm's will drop. Is that the way it supposed to be or my tranny is acting up? (4spd auto/O/D)

 

Yes, locking out OD changes the shift schedules. As does temp, load and a few other parameters.

 

mainly when dis-engaging the o/d lock out switch, it will unlock the convertor before it upshifts into o/d.