Buying oil & filter at parts store, the guy brought out tiny ac delo, think it was a 46....
Told him I wanted the large 61 and he said it was WRONG, wasn't listed in computer...
I looked under car and am sure that is what I've been using....am I ok?

 

the 5.3 l filter mounted on rear drivers side uses the shorter filter. a long one would be subject to damage

 

You are fine using the longer one. My 03 calls for the shorter one, been using the longer one with no problems.

 

FYI...........on a 2001 Tahoe, with the long 61, it is 2 inches from the bottom of the filter to the top of the cross member and the cross member is about 1 1/2 inches thick.
So you have about 4 1/2 inches of clearance.

 

A couple of points:
longer, clearance wise won't be too much of an issue if you are only highway driving and if it doesn't contact any frame parts while the engine moves within the frame mounting (yes the engine and tranny need room to move/flex within the frame)
Check the specs on the 2 filters to ensure the "features" are the same i.e. anti-drain back, clogged/blocked by-pass feature, rated for gas engines