Realtech214, what do you want from the shock? Do you want a very well controlled ride that is not as cushy as some, but offers the max in control, or do you want a floating cloud ride and control under "interesting" conditions doesn't enter the discussion? Or something in between? Try looking at each manufacturer's web site and read their description for what each of their shock model does.
Here's Monroe's Gas Magnum: "The Monroe® Gas-Magnum® truck shock absorber is designed for mid to full size, hard working pick-up trucks and vans. These units provide firm control without a harsh ride.
And, Monroe's Sensa-Trac"
Sensa-Trac shocks and struts adjust rapidly to changing road and weight conditions, delivering enhanced control with uncompromised ride comfort.
Sensa-Trac ride control products automatically adjust to changing conditions. They offer superior comfort for normal driving and deliver extra control when operating conditions get more demanding."
Monroe-Matic Plus: "AN ECONOMICAL REPLACEMENT ALTERNATIVE
Monro-Matic Plus shocks and struts provide an ideal balance of comfort and control for any driving condition:
Monro-Matic Plus ride control products feature Velocity Proportional Valving (VPV) technology that provides proportional damping based on the speed of vehicle-to-road impact.
Monro-Matic Plus shocks and struts provide improved comfort at an economical price."
I distill all this to say that the Magnum will give a very well controlled ride but maybe sometimes harsh. The Sensa-Trac is the best ride, and the Monroe-Matic is OK but cheap. You said, "just want a good on-road ride." I'd get the Sensa-Trac for your needs. All the other brands will offer similar choices; I'm not touting Monroe.
It is a surprise to have any stock shock last 100k. Likely the performance has deteriorated slowly, and you will really feel the difference when you put on new ones.
Sometimes it is a help to think about what shock absorbers actually do. They do not absorb shocks. They damp the rate the wheels can move up & down. The firmest shocks offer the most resistance to the suspension movement, which is just what is needed in tough conditions. The softest offer the least resistance which offers the best ride for smooth roads. More expensive ones presumably have better quality parts for longer life.