Ball joint replacement - just lower or upper and lower?

I have a 2002 GMC Sonoma with just over 100k on it. My mechanic has said that the lower ball joints need to be replaced and I trust him. A guy I work with says that I should also have the upper ball joints replaced at the same time, since it will save labor costs and alignment costs down the road. What do you guys think? Should I get all of them done at the same time? Thanks for you advice!

I take a conservative approach on suspension parts.
When one ball joint got loose on my '88 Accord I had all 6 replaced: two on each front, one on each rear.
Once off the others were noticeably degraded.

Depends on costs and your plans for the truck. If you expect to keep the truck for several more years doing all the ball joints makes sense. If you plan to sell the truck within the next 6 months just fix the bad joint.

I’ll probably own it another year or two. I’m leaning toward having them all replaced and I appreciate your input. Thanks!

These trucks are notorious for ball joint issues as they age 2WD or 4WD, doesn’t matter. I say replace all four and be done with it.

As a general rule, the ball joint that wears out the fastest is the one on the control arm that the spring is attached to. I believe in your case, that is the lower control arm so it would be the lower ball joints. But specific vehicles may have pecularities that changes the rule for them.

If it were me I’d replace them all and I’d also have a hard look at the tie rod ends when I was at it. Can’t be much more work to do everything but the parts might be a little high.

Some ball joints may never need replacement. If you have your alignment checked every two years, you should get good warning about worn out upper ball joints. Leave them alone and you will be money ahead.

Keith is correct on the lower ball joint getting the greatest stress and therefore the greatest wear. If well lubed and driven on well maintained streets all 4 should last hundreds of thousands of miles, though. If it were mine I would only replace those that are worn but none would ever lack for grease in the future. Same fir tie rod ends. And even without alemites the front end can be properly greased.