Yeah, the problem with coaxing any more power out of the 2.9 for less than it costs to put a 4.0, or even a 5.0, in its place is that Ford knew from the get go that a 2.9L engine was small, even for a ranger so they pretty much maxed it out at the drawing board. There isn't really any way to get a significant amount of extra power out of it without doing more work and spending more money than the 4.0 swap would take.
You can't chip them because 90% of the time it puts them in fail-safe mode, you can't blow them because the heads won't handle it, a bigger TB can make them run screwy if you aren't careful and doesn't give you huge gains in power, it was designed to run with its emissions controls in place, so taking those out doesn't help any, and it usually hurts you, if you bore and stroke the 2.9 block you get paper thin walls and more compression than the heads can handle.
Your truck is a 90 though, so for you a 4.0 swap is really a matter of taking a 4.0 engine, bolting it up and plugging it in. Just need a 90 computer too. That's a lot less than most of us needed to do (or still need to do) to get a 4.0.