Deep Slotting

I have a job to quote that requires 15 slots 3 inches in length in 6061. Each slot is .29 wide by 2.9 deep. The fin between each slot is .06. the slots are open on each end.

I am milling a demo piece right now using a relieved .25 3 flute alumistar with .25 flute length.

It doesn't seem to unhappy but it's pretty dang slow. Obviously, when I run actual parts I would start with a stub and work my way up in length while I decrease feeds and speeds.

Have any of you guys found plunge milling to work in an application like this? Perhaps milling the first inch or so with regular feeds/speeds then switch over to a plunge pattern? I would still only be able to plunge .075 or .1 at at a time before I finish mill each fin each step down.