Japanimports from that era often had high-revving engines that unnerved people who were used to the more lumbering redlines of their American counterparts. It took me a long time to convince one of my friends that winding his CRX up to 5,000 RPM not only wouldn’t hurt it, but was more than 1,500 under redline.
It can get especially fun in the cars that have no tach, which I’d be willing to bet includes your truck.
But here’s the secret: The engine has a rev limiter. Your redline is, if I recall, somewhere around 5700, which on that motor is going to sound very high when you’re actually doing it. You’re pretty unlikely to ever get near it unless you give it to a teenager who wants to pretend he’s in a race car. And if you do get to it, the rev limiter will kick in and stop you from overspeeding the engine, and you’ll know it’s kicked in because the car will buck and you’ll hear the fuel being cut off and turned back on in rapid succession.
I highly doubt that 3rd gear at 40mph is anywhere close to 5,000rpm, so you’ve most likely got a lot of headroom shifting at 40.