Thanks for the replies, folks. I just came back from the pro shop with my bow.
Here's what he told me: (maybe he's also learning some about these different combos and carbon arrows?!)
--The D loop WITH a retention rest makes it hard(impossible)to tune with my GoldTip arrows. They tried the BD Zapper and others and couldn't get the arrow to shoot straight. Apparently the loop makes my Jennings CM Xtreme very sensitive to spine strenth. Gold Tips are 5575s and I'm set at around 58lbs.
So now...the D-loop is gone - I'll be shooting off the string - and I'm back to a two-prong rest (now a nicer Quik-Tune one) even trade and no charge for the work. To my bowyer's credit, it was I, the novice, who wanted the D-loop installed as well as the biscuit rest. I'm going to try a NAP (I think it's a 'Quik-Flip'?) arrow retainer to keep my arrow in place and otherwise Keep It Simple (stupid) from now on.
I'm glad I decided to resolve things before shooting at a deer! I'll shoot tomorrow and give a report once I see how it shoots.
--Dan

Dan