I have a Payne Category 1 forced air gas furnace. Seems to be working properly but only blows luke warm air. Burners ignite properly and the blowers all work fine, just very little heat. Replaced the filter, foil taped all duct seems and the furnace is only 5 years old. Any idea's?

Lil more info...
Model #: PG8MAA036070ABJA
It's a natural gas furnace and the whole unit sits in the crawlspace under my house

Have you stuck a thermometer in or near a supply duct to see exactly how warn the supply air is?
Make sure the returns are open and nothing has them blocked off or restricted,while you`re at it also check the temp of return vent see what the difference is
Go around the house, windows, doors,everywhere cold air might be coming into the home, unwanted
Is this the 1st year you`ve had this problem?
,, get back to us and let us know