This week i've been building a small end table that is essentially just a mitered plywood box. On the first go around, i set up the blade to 45 using the wixey gauge and then cut all the bevels. I go to put the thing together and my angles are off. The sides angled in about 1/8" over 6 inches. Each bevel was off by about a half a degree.

So then i got to trying to figure out what was wrong.

I checked the wixey gauge first. I put my starrett combo square in the vise, set the gauge on the face, zeroed it, then put it on ruler. it read a perfect 90. I checked the starrett for square using the draw a line and flip it over draw another technique, and it was square too.

Then i went to the saw. The blade is perfectly square to the miter slots and the fence. I set it up only a few months ago, and i rechecked it tonight, at 45 and 90, rotating it and measuring off the same tooth, and it was all still good.

I got a piece of wood, put the blade to 45 using the wixey, checked it against the 45 on the starrett, it was flush. I made a cut, put the two halves together, and..it was acute. off by about a degree.
I put the wixey on the table, zeroed, and then on the bevel cut, it read 44.6. I put it on the blade, it read 45. I move the blade to 45.4, make a cut, put the bevels together and its a perfect 90. So at least now i know my cuts are off by .4.

What the heck causes this!? Could the blade be off? I just put a new blade on this week, an Irwin Marples one. I don't know what else to check at this point.

Thanks in advance for the help.