The G.O.A.T. tight end partnered up with USAA to deliver a 4-door truck to specialist Jonny Flores who served four years in a field artillery unit ... where he worked as a .50 cal gunner, among other jobs.

"Today I'm helping USAA give away a recycled ride to a deserving US military veteran," Gronk said on Tuesday.

"This is gonna be awesome. About to surprise Jonny."

The video of Gronk surprising the Purple Heart recipient in Tampa is amazing ... and from Flores' reaction, he had no idea he was meeting the Super Bowl champ.

"No way!" Flores said, clearly in shock ... "What a surprise!"

Then, when Gronk showed Flores the truck ... he was so stoked!!

It's a feel-good story for a man who has sacrificed mightily for his country. Flores was badly wounded after a vehicle he was in drove over a pressure-plate IED (improvised explosive device) on July 4, 2007 in Baghdad, Iraq. He ultimately had his left leg amputated. He also sustained other injuries in the attack.

Flores, who uses a wheelchair, will now be able to move around much more freely ... because we're told the ride was retrofitted and modified for his mobility needs, including installing a wheelchair lift.

"This means a lot to me," Flores said, "Being able to get my independence and get in and out of this with ease, you know, with no help. That wheelchair thing is something else!"

"This is a game changer. Oh my God. I can already see how many trips and things we're gonna do with the family. I'm so excited. I can't thank you guys enough for this man."

It's all part of the USAA's celebration of their 100th anniversary serving the military ... and the vehicle was the 87th car they gifted in 2022, Gronk's jersey number.

Gronk played 11 seasons in the NFL with the Patriots and Buccaneers. The 5-time Pro Bowler won 4 Super Bowls before retiring in June.