My transmission won't upsift
a few months ago about a week and a half after having the radiator changed I was driving normally then all of a suden iT was like I was driving but it seemed like it was in a lower gear or had the breaks on so I hit the brakes hard it it made a loud clink sound and went back to normal since then some days it takes a long time to shift gears (sometimes it gets to 2000-3000 rpm before it will change) then on Saturday it wouldn't change until it hit 3000 rpm and I took my foot off the gas petal now it won't automactically upsift gears at all

we dumped the trans fluid and replaced the filter and put new trans fluid in (4quarts like the Haynes manual said) but it is still below the min line on both sides of the dip stick

it will cycle in and out of gears no problems no delays but when you drive it it will not upshift automatically

I tried this today after refilling the trans with 4 quarts of fluid and no auto upshift I pulled over put it in first and it will manually change from 1 to 2 but not 3rd or overdrive so I put it back to second went round a round about and then it upshifted from 1 to 2 on its own but even when i put the lever to drive it wouldn't change up to 3 or over drive

what else could it be I've spend close to $3800 on the trailing arms and radiator and I really don't want to have to spend another $4000 getting the tranny rebuilt please help any suggestions would be great

thanks in advance