When i first bought my truck the rear diff. was clean and free of any lubrication marks now the entire rear diff. looks like it was coated in a thin film of gear lube. So my question is i know a little bit of seepage is normal but when is it to much.

My '01 only has 40K miles on it, but there is no diff. seepage front or rear. It may be because of your higher mileage, but I think any seepage is an issue unless there is some serious articulation of the axles (i.e. off-roading) that may cause the cover to flex or warp. Check for pinion seal leak, xfer case or rear trans seal leak that may be "slinging" oil back on the diff. I think the gasket is actually an O-Ring, and during a service it may have been pinched and your are not getting a good seal. Last but not least verify the bolts on the cover are at the proper torque...one too tight and another not tight enough.....could contribute to the problem.
JP

If its only seeping around the cover, take it off and replace the $15 gasket. Good time to change out the fluid and clean any junk out of the bottom of the housing. OEM still uses paper gaskets that get saturated and over time start to seep.
Or, you could go high end and get an Aluminum diff cover with an milled o-ring groove that will never leak.

As long as it isn't dripping or slinging it elsewhere, it should be fine. One drop of oil will spread immensely across a surface on it's own. Add to the formula the heat of the differential, and the warm air from the engine/exhaust, and it will spread even further.

On my trucks, if it's just a seepage issue, I usually let it slide. I consider it GM's "Rust Protection Plan". Cosmetics are out....

It seems pretty uniform around the filler hole and the paper gasket area. But it just started to do this around 65000mi. It started when i came down the MS coast for a little bit. Could it be from their crappy roads, it is so bumpy down here i almost cant stand it.