Changing out the 250 w hub motor to serious power about $189 for a DD 48v 1000w with controller, brake handles & throttle. Plus a new 48 v battery, $400-700 depending on how much range you want. 3 miles of 8% is nothing, I wouldn't worry about a DD on that. My DD 1000 W would start me at 330 lb on 15%, (7/8" rise on 6" level) but it used a lot of electricity on all the hills I ride on. It would start dropping power due to minimum voltage uphill on the last couple of miles, whereas the geared hub gets me there with about 20% left.
If you can get a 48 v 1000 w geared hub even better, but I might have got the last MAC 10 front kit luna had at $500.
If you maintain your 36 v battery a geared hub can be bought from ebikeling and others. Most don't carry 48 v geared hubs anymore.
I'd say buy a 48v battery from lunabikes ebikeling or hicks says californiabike is good. I got **** for batteries from 4.8 star vendors on Amazon & ebay, ended up with quality 17AH from luna for $630.
My derailleurs & chain are OEM, 24 speed, 11-32 on the back, 30-42-52 on the front. Try to find a 11-32 in 7 speed freewheel, I never could. You'll have to go down to 7 speeds rear if you buy a DD rear hub motor, that is the max they will allow IMHO: without spreading the frame, which one should NOT do on an aluminum frame bike. Cast aluminum doesn't bend like hot roll steel.
Again, the advantage of a kit, you can buy 1000 W, unlike whole bikes that can't be sold in a lot of states with that kind of power.
If I start dead on 15% grade both motors will get up to 4 mph at 300 lb, but since we have rollers I bring in a lot of momentum from the previous hill and average about 9 over my 30 mile ride. Peaking at 30 mph at the bottom of the steepest grades.
