Shift Automatic I drive my car down the road and it shifts fine from 10 to 20 and then 20 to 30! and when it hits 30 it roars and then it shifts back down to 2! and it sounds really loud!

You have a failed transmission.

i take it is a automatic check gearbox transmission fluid or the torque converter may be at fault

manual or auto
bet automatic.

alldata.com has this.

but really you don't need to read that.
cable off trans.end.
set the transmission to say, drive. position at the t actual trans manual shift lever on side of trans. (the PRNDL switch may be here)
count the detent clicks., (easy huh?) to drive PRND bingo there.
then attach the cable and get it to the Drive marker in the cab console.
the lock it all down.
the test all gears. park and neutral , in drive way, not on road yet.
if all ok, hit the road.

do you mean you changed the engine speed sensor for the auto box ? works off the engine rev's this is not on the same line as the rev counter it counts the rotations of the shaft spining.

Your shift cable has stretched.Replace cable.

Inspect your shift linkage if it has loosened or misaligned, either at the shifter itself or on the transmission.

possibly a transfer case motor problem make suer you are in 2 wheel drive,try shifting button from 4 wheel to 2 wheel drive and make sure your tow haul switch is off on the end of the regular shiter

the bearings in the front end differential are probably going out.

That would be a 3t40.sounds like you got a final drive problem if you can hear it shifting.Possible broken drive axle?

could be a faulty solenoid, scan the TCM for faults and drop the sump for contamination