I need a interchangeable transmission for a 99 taho rwd

It's not a year thing but a numbers thing, the numbers must match each other or it won't work. I have found that sometimes the late year previous will have the same number or even the next year up if early in production will also have the same number. Good luck.

Will a 2003 Suburban transmission fit a 2009 Tahoe

Nope. It might look like it will but it is totally incompatible electronically.