A couple of things..your spedo seems way off, check it over a 10 mile section of hy using the road mile markers holding MPH on your spedo. I think its about 8% low which if its is your getting close to 18 now.
Its Very hard to get much better than 18 at 70mph. 16.5 mixed is great! Plus you have a lifted CCLB!!
TW doesn't use 20-40-60-80 bs settings on his chips so you might want to pull it and see what you have, if its his send it back for his new burns.
Any way of finding out whos inj. you have and if their stage 1's or 2's? Old style 2's won't get you the best MPG but Tony can help.
Unless you have a 17* HPOP you are running low on oil and your atomization isn't as good as it should be which can cause more black smoke..less MPG.
Cary