I just bought a '98 Tahoe that has 175,000 miles w/ 5.7 litre V-8. The transmission was a little low on fluid so I added about 1/2 a quart then it started shifting real hard 1st to 2nd and 2nd to 3rd. So I went and got a new filter and fluid changed it out and seemed to be shifting nicely and once it got good and warmed up it started shifting hard again. I also put some Lucus Trans. conditioner in it. Is this something I can fix or am I going to have to get it rebuilt?

You may have a shift solenoid sticking or a bad connection leading to the transmission. Pull the connector and check pins for corrosion. otherwise it may work its self out with the fluid change. Give it a couple of days and if it doesnt change have a trans shop or someone witha scan tool check the solenoids. Check all fuses.
It is also quite possible that the previous owner installed a shift kit to tighten the shift points but that is reaching deep.
Usually these trans either quit moving or start slipping real bad when there done.

I just bought a '98 Tahoe that has 175,000 miles w/ 5.7 litre V-8. The transmission was a little low on fluid so I added about 1/2 a quart then it started shifting real hard 1st to 2nd and 2nd to 3rd. So I went and got a new filter and fluid changed it out and seemed to be shifting nicely and once it got good and warmed up it started shifting hard again. I also put some Lucus Trans. conditioner in it. Is this something I can fix or am I going to have to get it rebuilt?

I would say the hard shifting is a pressure problem....could be a rebuild is required or just a part replacement...

the transmission shop should be able to check this and report how much to repair...

as I hope you know the transmission must be at or slightly below the full mark when hot.....on level ground....if its over the full mark you will get erradic hard shifting..

i have the same problem, i just found a site that may help us out. http://www.fullsizechevy.com/forums/archive/index.php/t-94725.html once i get money im gonna try to fix my tahoe.hit me up if u fix yours befor me.......

It could be possible that you are getting a P1870 code which causes the tranny to increase line pressure to avoid damage. This is called "limp" mode. A harsh shift is the result.

A worn TCC regulator valve is a common cause of P1870. The valve body can be repaired without dropping the tranny.

With 175K miles, the tranny could also have worn clutches, sun shell and 2-4 band.

If you just want to fix the harsh shift, you need to pull the valve body or find a shop that will repair the valve body.

//2000CAYukon