I have a 1995 chevy tahoe and I noticed the tires were wearing on the outside and that they were leaning out on the top, I was told to replace the ball joints and I did and still have the leaning issue, what else can it be?
That's an alignment issue. You were observant to notice that tire wear. If nothing else has been done, the most likely cause is sagged springs. If you have torsion bars, the alignment mechanic will measure and adjust the ride height before making alignment adjustments. If you have coil springs, they either need to be replaced if they're bad enough or the alignment can be set as best as possible. Even when the numbers are perfect, if the ride height is low, the suspension will travel through the wrong geometry and there will still be excessive tire wear. You will not see that as shoulder wear on the inner or outer edges, but tire life will be reduced by maybe 10 to 20 percent due to the tires scrubbing sideways as the truck bounces up and down going down the road.
That excessive positive "camber" will also cause each tire to want to roll in the direction it's leaning. If both tires are leaning out approximately equally, the truck can still go straight when you let go of the steering wheel.