Tart flavor in Wheat pumpkin ale ?

I posed this question in a thread I started about a pumpkin ale that I brewed last month and unfortunately I keep getting overrun with people asking me questions about how to brew their pumpkin ale and no comments on what might have caused the slight tartness I am tasting in my reasonable young pumpkin ale. Here is a link back to the original thread:
https://www.homebrewtalk.com/f37/another-pumpkin-ale-thread-tis-season-271272/

My recipe is as follows:

Fermentables / steeping grains
7 lbs. Wheat LME
1 lb. Charamunich Malt
0.5 lb. Crystal Malt (40L)
0.25 lb. Belgian Biscuit Malt
1 cup brown sugar, light
1/2 cup molasses

Hops
1 oz. Willamette (60 min)
.5 oz. Stirling (10 min)
.5 oz Stirling (5 min)

Other Ingredients
60 oz. Libby's 100% pure pumpkin, roasted at 350F for 30 min. and added with the extract.
Spices (I dont remember exact quantities of each off the top of my head) are Cinnamon, Nutmeg, Clove, Allspice, and Vanilla extract.

Yeast
US-05

O.G. 1.060
F.G. 1.016

anyone have any ideas what could be causing a slight sour/tart flavor in this beer? it is very mild and does not detract much from the overall flavor of the beer but I can notice it so I would like to know where it is coming from.

My pumpkin ale this fall had a bit too much pumpkin (around 60oz) and had a vegetative taste to it, maybe that could be interpreted as tartness?

My pumpkin was in the mash as opposed to the boil, however..

That could be the case but I have always expected the vegital flavor to be more like cooked vegetables like cabbage or broccoli. maybe I could back off a bit next time with the pumpkin and filter it out of the wort before fermenting which I have thought about doing anyway. unfortunately until I figure out how to go AG in my townhouse, I wont be able to filter out the pumpkin before the boil. I'm working on that though.