I don't think so. I'm not finding anything on that option but then Dodge has never been known for fuel mileage. I think the 6.1 is just made for raw power propelling the GC from 0 to 60 in under 5 seconds, top speed over 150 mph and mid 13's in the 1/4 and maintaining 4wd as well. It's not bad for a stock vehicle. Here are some links:
http://www.americancarfans.com/news....id/2050323.002
http://www.suekeen.com/GrandCherokeeSRT-8.htm
http://www.wkjeeps.com/wk_srt8.htm
https://dodgeforum.com/m_174858/mpag.../tm.htm#175196

 

I have thought about a 6.1 swap also, but my only concern is the torque through the T-case (for us 4x4 drivers)........ and while we're on the topic of hemi swaps, why not just wait til 2008, when the Challenger comes out with the 6.4 Hemi with 505 hp and 450+ torque (DROOOOL!!!).