The filter for your truck (PF48) has a built in By-Pass, If the filter were to clog completely, The By-Pass will open & still have oil pressure.
If the aftermarket filter has no By-Pass, And clogged/collapsed...That could cause this. The odds of the planets aligning in such a way is far fetched.....You would have to buy the wrong filter that miraculously screwed on, Then Clog.
I agree with Brian F., Install a mechanical gauge & see what's going on, A "Diagnostic Trouble Tree" will say to do this first.
The down side is most oil pressure test sets only include NPT fittings, LS engines use Metric "Gasket" Straight thread fittings on everything.
Here is a fitting that will adapt the Metric port to 1/8" NPT
http://www.summitracing.com/parts/atm-2268
GM dealers have a 12 month 12,000 mile warranty on repairs, But this may or may not be related to the problems your having.