5400 is about 500 rpm low. Ideal is 5900-6000, but your cruise mpg may not change if you go to 3x16x20.
There are lots of factors that enter the best cruise mpg. Just read the various OB mfgs test.Try some other rpms like 3800and 4200.
Reread WCC test data NOTES about no electronics, no gear, ie like outriggers, fishing rods in rod holders,anchor ,anchor chain.
1. Did you bottom paint it? Harry and Us have gotten very good results with Micron 66 with very low mpg reductions and application life. We know for a fact that another cheaper Micron gave less gas mileage, We only left it on 4-6 months.
2. Were you going into a head current, ( go both directions)
3. Was it a hot + humid day = less HP for a given rpm.Yam and Honda prop tests were Jan. Feb
4. 180 fuel x 6.3 lb/gal= 1134 lbs
5. 35 g fresh water + 15 gal waste =50g x 80% x 8 lb/gal= 400 lbs.
6. How much additional equipment have you added .If you did you probably put it up front making it more nose heavy.
1. No paint, lift kept
2. Tried both
3. No, actually it was a cool day low 70's
4. Yes, I had 180 fuel
5. Yes, I had about 35g fresh water but waste tank is empty
6. No additional gear except for electronics... maybe 15-20 pounds total with half that in rear due to transducer
To address other posts:
1. No riggers, no rods, no gear of any kind
2. Yes, I'm coming up short on RPM without gear so it will only get worse (with some mitigation after break in).
3. The good news is dealer is going to put some 20 pitch props vs. 21.5's and I'll report back results in a few weeks
4. I don't believe test results either
5. I'll fill the tanks and try a long trip soon to test accuracy of meters... will let you know what I find