You could do it but it would be much cheaper to just buy a good used 1990 GMC 4+4 truck and drive it.
It will as long as the 98 truck is a 4-wheel drive too. 4-wheel drive and 2-wheel drive transmissions are DIFFERENT and will NOT INTERCHANGE.
The transmission is not a 2wd or 4wd. There is way more to it than just changing transmissions or final drive units. This is a really bad idea. Sell this truck and purchase a 4wd. Look under a 4wd Chevy truck and compare it to your 2wd. You will easily see that the components necessary to convert a 2wd to 4wd are many. Forget this idea.
The 2012 RAM 1500 has rear wheel drive.
The 2014 RAM 1500 has rear wheel drive.
The 2011 RAM 1500 has rear wheel drive.
The 2013 RAM 1500 has rear wheel drive.
pull lever to put into 4wd
The 2010 GMC Sierra-1500 has rear wheel drive.
The 2006 GMC Sierra-1500 has rear wheel drive.
The 2010 Chevrolet Silverado-1500 has rear wheel drive.
The 2004 GMC Sierra-1500 has rear wheel drive.
The 2011 Chevrolet Silverado-1500 has rear wheel drive.