I'm concerned with "will hardly stop the truck". I'm assuming you have thoroughly bled the entire brake system? Even without vacuum boost, you should be able to almost lock up the brakes if you stand on them hard enough. If the brakes are ineffective, and you've change the booster twice already, you need to investigate further for trapped air issues, or collapsed lines to one or more calipers/wheel cylinders.
I do not know if this will apply to a Dodge Dakota, but this is what I once experienced with my GMC:
in short, there was an issue with one of the front ABS sensors (which are in the hubs) and INTERMITTENTLY, always at a slow speed, the message that the sensor was sending the controller did not always correspond to what was actually happening, and as a result the ABS would activate when it was not supposed to, and stepping on the brake pedal would be like stepping on a brick. Basically, to depress the brake pedal enough to apply braking action, I had to practically stand on it to drive it down. Note that there was NO "ABS" light illuminated on the instrument panel when this was occurring.
The first thing I did to temporarily alleviate the issue was to pull the ABS fuse from the under-hood electrical box, which did illuminate both the red "brake" light and the amber "ABS" lights, but did effectively disable the ABS system. I did finally wind up replacing that hub (wheel bearing was worn out) and that ultimately is what the fix was.
Again, this was not a Dakota but an '02 GMC and this very well may not be applicable, but one thing you could do to eliminate it from the list of possibilities is to pull your ABS fuse and see if you have better brakes without the ABS activated.