Want to change gears in rear end for posi traction in a 98 gmc25000 is this possible?

It is possible, you just have to know what gear ratio you have in your Sierra. I had issues with my son's rear differential and did the Salvage Yard and picked one up for $250.00 with less then 45,000 miles. Remember new cars end up at Salvage Yards also.

Here are the Pro code for the rear ends to your Sierra and you can match one up at a Salvage Yard.
GQ1 -- AXLE REAR, STD RATIO
GT4 -- AXLE REAR, 3.73 RATIO
GT5 -- AXLE REAR, 4.10 RATIO
GU4 -- AXLE REAR, 3.08 RATIO
GU5 -- AXLE REAR, 3.23 RATIO
GU6 -- AXLE REAR, 3.42 RATIO
G80 -- AXLE REAR, LIMITED SLIP (POSI TRACTION)

HC4 -- AXLE REAR, 4.56 RATIO

Open Your glove box and look inside it. Should be a list of codes on the bottom.
Example: GU6 G80 According to that, you'll have a 3.42 posi

Good luck and keep me posted and call around Salvage Yards, there prices will differ from one to the next salvage yard and don't ask them for a posi rear end. The cost will you more, just search all the SUV's and look at the pro codes in the glove box. Hunt, most awd system SUV will have the G80 rear end.

Good luck and keep me posted.

It's not the gears that would need to be changed to get posi traction. It's the actual differential (Which the ring gear bolts to). I don't know which size rear end comes with that model truck but if you can find out, you can see what's available as far as differentials go.

Any transmission shop should be able to perform this swap for you.