Gear ratios 83 k1500

[Adam1983Sierra]

Anyone know the stock gear ratios of a k1500 from 83 or at least a way to tell? Looking to go to a bigger tire, but don't know if i want to rehear my diffs. Also what trains would I have it's an auto 3 speed I believe it's a th400 but idk.

 

[CSFJ]

Need to look at the shape of the pan to identify it. Google image GM transmission pans. I tried to upload a chart I have, but it tells me I have the wrong file extension.

 

[DoubleDingo]

There is a thread somewhere on here that explains how to figure it by jacking up the rear axle and turning the tire by hand and counting revolutions compared to the driveshaft. But I haven't seen it in years and I forgot where it is located. One of grizzled squarebody forum vets should know which thread I am talking about. HotRodPC wrote it if I remember correctly.