You said you replaced the battery but you've only got 12.26? - I would expect a good strong 12.6 before starting.

What's your alternator output? - You might want to check when you first start - turn on a full load (AC/lights/radio/and every other electronics you can find), recheck, then take her for a drive to get Inga good and warmed up and then recheck again.

I've seen alternators deliver a "minimum load" (about 12.4-12.8) and when warmed up drop output. The testers at the part stores (zone/advance/oriley) rarely fail these - but they will not keep your battery at full strength. If charging correctly - you should always have at least 13V out of your alternator even under the heaviest load.

Also double-check your exciter wire!! - it may be causing your alternator to not work. The heat from the exhaust manifold is "heck" on the insulation. If not delivering good voltage, your altenator "may work" at some RPMS not others (I think I read that somewhere on this Forum)

If the Exciter is ok it might be a diode in the alternator that is shot.

(replacing the Alternator and re-insulating my exciter wire with Liquid tape seems to have cured my no-start. And I'm still running the same 6 year old battery!!!)

Hope that helps.
Charles