I think the SyTys are more reliable. When was the last time you heard of someone with a SyTy blowing their transfer case? Next to never. Most stock trannys last quite a while too, I'm running 12.5's on mine with 50K and no indication of the tranny going south yet. My friend has 135K on his original tranny (and motor) with about 2500 launches (!) running mid twelves as well, and ONLY in the last 2 months has his 2-3rd shift begun to slip badly. Maybe we are just 2 lucky people but I think the SyTys generally last a good while if taken care of. Now if I was running 11 seconds I am positive my stock tranny would be taking a shit ASAP and it probably will anyways due to accelerated wear but that's the name of the game. In addition, people run 10 seconds on the stock suspension, driveshafts, and front and rear end, and they aren't known for breaking often either. I think the difference is the S-series platform is based for commercial hauling, that kind of crap. Whereas the DSM was probably designed more for a light passenger car. So the SyTy ended up being built more stout just by coincidence IMO.
so keep the jimmy and buy a ty too.