I never trust them thermo's usually wrong! Get yerself a digital one fer grate temp, put the probe through a tater an set it on the grate, now yall know what yer temps really are. They can be tested by puttin them in boilin water an dependin on yer altitude should be in the nieghborhood a 212°.
I never use a store bought rub, make up my own, many a the store bought ones er sugar an salt.
Do some searchin an find a recipe that sounds like it got stuff in it ya like then play with it some. I rub my ribs an wrap in foil the night before, never have a problem, BUT, my rubs don't have alota salt in em.
The method ya usin is fine some folk call it the 3-2-1 method, but it is just a guide line, I usually do the 3 then bout 1 1/2 an 1/2. Ta check them ribs ya look fer the meat ta be pullin back from the bone then pick em up with some tongs, they should flex real nice.
Also, I don't put sauce on mine, but I would save that fer the last 20 minutes er so ifin ya feel ya need it.
Lets see, yall said baby backs didn't ya, I'd do more like a 2-2-1 on them. 3-2-1 be fer spares.
Don't give up, keep at it, yall will figure out a system that works fer ya, ain't no suck thin as a bad rib, just good ribs, great ribs an holy cow them er great ribs!