I believe 3.08 was only offered in the diesel Burb for the first few years. 3.42/3.73 are the other possibilities.
Most 3/4-tons have 4.10 gears and a TH400 (not OD). They're okay for city driving, but suffer on the highway. I swapped a 3.21 axle into mine for this reason.
IMO, look for a '91 3/4-ton. You avoid the fragile 10-bolt and small 1/2-ton brakes, and get a 4L80E (OD trans).