good background on Luebke here
A pineapple can could bat .300 in Tucson, and similar conditions favor hitters in other PCL haunts. Among those is Salt Lake City, where Luebke fared so poorly in a game last summer that a non-Padres scout, stumped by the fuss over him, couldn't write up Luebke as a prospect. Some pitching prospects can weather life in the PCL. Others lose confidence and good form. Petco Park, conversely, nurtures a pitcher's confidence. It's especially hospitable to lefty pitchers who can keep the ball out of the left-field seats.
Luebke justified the move to relief. He has given the Padres a 3.23 ERA in 39 innings across 29 outing. He took his lumps in early April, but since allowing six runs to the Reds on April 12, he has been Steve Howe-like with a 1.65 ERA in 25 games. He struck out 35 over those 32.2 innings. Safe to say, such results build confidence.
Tomorrow, he returns to starting. He draws the lefty-laden Braves.