I finally succeeded in getting my hard throwing lefty through success mode to the Majors - even made the MLB roster on opening day!
A couple changes: I only have 3 pitches: 4-seamer, drop curve, and a hard shuuto (couldn't resist). And I really only focused on the first two: DC rated 4, HS rated 2. Final ratings were B Stamina, C control, and 93 top speed.
Not sure what I did right, exactly, but being nice to Marvin might have helped. He went Santa Claus on me at one point, throwing like 7 items my way, which I was able to sell for some nice equipment.
Oh, and the drop curve is a filthy pitch. I averaged 2 Ks per inning with that thing during spring training. Next up: MLB Life Mode