Installing LT's AFTER a tune: retune a must?
 

Going to install a set of LTs in my cammed 4.8 RCSB while it is down getting regeared (4.56's)

It had cats and manifolds when tuned the first time- is a retune a must after going to LT's and catless ORY?

At a min you'd need the rear O2's codes shut off. You'd benefit from some tweaks from the LT's, but otherwise its not absolutely mandatory.

Like DDN said its not mandatory just helps to make it run optimally and get rid of the SES light. I drove mine untuned for months after the install no problems at all.