2004 Kia Sedona Engine is not accelerating properly after w

We just had the drive belt replaced along with the AC compressor & clutch last week & then the belt tensioner replaced today (for free as it was not broken before we brought it in), then after a little driving around town, about 10 or so miles, I noticed the low gas light came on so I stopped & filled up (at a place we normally go, non-ethanol, 87 octane). I believe the van has a 19.5 gallon tank & I put in nearly 18 gallons (I filled it as full as I could get it). I drove less than 5 miles after that & then all of a sudden noticed that the engine was not running properly. When I try to accelerate the engine does nothing, but then it suddenly jumps as if the gas finally made it to the engine. It continually does this, sputtering, hesitating, then jumping. No matter how far I push the accelerator, the van will hardly accelerate and will just "jump." It does this whenever I try to accelerate, and is smooth if I just let it "coast". Is this a gas related issue? Everything was running perfectly smoothly before I put the van in the shop today and definitely before I filled up with gas. Please advise on what the problem may be and how to remedy.