5.9 Magnum Torque motor build?

Absolutely till you drive it and see if you can give up any grunt torque (a more duration cam)
Theoretically you could go to a cam with the same seat duration with more lift and more area under the lift curve giving a "deep breathing" effect
and /or high lift rockers (either would merit new springs and most likely machine work on the heads for keeper clearance- I know some grind their keepers...)
but neither would be cost effective
ditto with stock exhaust vs headers
at this point IDK if block hugger headers would fit on both sides- depending on the steering box etc so U have to get it in and eyball
to really help the low end you are looking at long tube headers- anyone make them for your truck? IDK maybe with a 2 1/2 collector
Tri Y would be better than block huggers- but still- for now- save your money There is a program calld Pipe Max which I would use B4 looking at headers
you need to find those who have built in the same rpm range U are shooting for and not chase more rpm= more absolute top end horsepower then have to regear and all that
My old Dakota has 3:54 gears RV converter and I tow with it
most any cam change hurts the starting up a hill with 4 horses or pulling the boat out of the lake grunt
1.7 roller rockers would give some gain but when I add up going to an adjustable valve train, springs and pushrods it takes all the fun out of spending money
maybe when I have to do a major rebuild- but then I'd go stroker