You might be able to get away with routine maintenance for a while and not need to rebuild your engine. However, if you’re noticing that there is more smoke coming from the tailpipe than usual or the truck isn’t as powerful as it used to be, then it might be time for an engine rebuild sooner rather than later.
If you are looking to replace your engine with good aftermarket engine then autovehicleparts cab be good to buy used engines for sale - https://autovehicleparts.com/used-engines/