The gold standard for checking the wrap is the endoscopy, though even that is inconclusive. When my stomach was herniated to over 50% with nearly no wrap left at all, all the endoscopy showed was a '"defect" at the site of the wrap.
An upper GI/barium swallow would be helpful to see if you are actually refluxing right now, since it takes months of reflux sometimes before you start feeling it. But, it cannot give you a definitive answer.
Another possible test that might help is a CT with oral contrast, which might actually catch a herniation, but is unlikely to clearly outline the wrap itself. It really depends on whether your initial surgery was necessitated by hernia or by a weak LES.
The only way to "see" the wrap is through surgery. Having gone through this three times, I can tell you that during each of the redo procedures, not one doctor gave me an accurate reading on the wrap itself. Some overestimated the failure and some underestimated it -- both by very wide margins.
As for the shoulder pain, I just don't know. I would hazard a guess that it is unrelated to this surgery.
Diagnosed with GERD 5/99 -
Lap. Nissen 7/00;
Lap. Nissen w/ Mesh Repair (>50% Herniation) 4/10;
Lap. Nissen, Rivet Mesh Repair & Gastropexy 7/12