Post Malone got an old Ford Explorer swagged out, and the sick job upped the formerly beat-up SUV's value by at least $73,000!

Sources connected to the makeover tell us Post had the idea to customize a '92 Explorer ... so he bought one for $1700, and sent it over to West Coast Customs to make it happen.

We're told it took 6-8 weeks to add new lambo-style doors, candy custom body paint, 26" wheels and tires with spinner rims. Post calls it his "Texas Slab" to honor his Houston roots.

Fun Fact: "Slab" stands for vehicles that are slow, low and banging.

The new whip will definitely be banging ... based on the massive speakers WCC installed.

Post's baby will be featured on an upcoming episode of the reality show "Inside West Coast Customs" on Velocity. 

WORKIN' ON THE WHIP
West Coast Customs Inc.