O2 sensor CEL's - Help!

[brewerbry]

I recently had to rebuild cv joints on my 1997 tip boxster after several spirited DE days (and a couple off track excursions). I chose to pull the whole axle which required taking apart the exhaust. I got it all back together and am now throwing 3 CEL codes all having to do with the O2 sensors. I have the following codes:
P1119 - fault code 5 - oxy sensor heating 2 ahead of cat - below lower threshold
P0154 - code 18 - oxy sensor ahead of cat (cyl 4-6) - interruption of signal
P1115 - code 13 - oxy sensor heating 1 ahead of cat - below lower threshold

What the heck is the problem? The exhaust is tightened well and I do not hear any exhaust leaks. I have not changed anything else during this repair.

The car threw these code one time on the way home from a DE day but I cleared them and they never returned until now.

I have cleared these codes several times, driven the car a fair amount (50 miles or so) and the codes keep coming back.

HELP! Please!