I appreciate your feedback Remy.
I realize the weight will be a penalty, once the system works I plan to upgrade the batteries to lithium. I have extra weight capacity I'm not using. The battery weight with the lead acid will be about 10% of the total truck weight. If the fuel economy breaks even with the lead acid batteries then I will gain with lighter batteries.
Factory hybrid trucks use the engine to charge the batteries, I will be charging by plug in only which should also help the economy.
The axle is a drop in replacement for the solid tube axle currently on the truck. The current steering, springs, brakes and wheel hubs all work. it's a very easy swap. I think the hardest part will be incorporating the throttle pedal to run the electric motor. I have been told forklifts use a tps with a 5v reference signal the same as the truck uses so I may be able to just tap into the return feed.
I don't do much city driving. 99% is country roads with 80kph speed limit, Less than 100km/day. The truck weighs 17,000lbs now and is good for 20,000lbs. I currently get approximately 25L/100km or about 9.5mpg. I'm not sure the extra weight will lower that very much.