99 GMC Yukon with 5.7 vortec won’t stay running

I have a 99 GMC Yukon with the 5.7 vortec. Just
got it out of the shop and had fresh oil change. It
sat for about a month after of getting it back and
will start right up just fine. But after about 10-15
minutes of it running it starts sputtering and the oil
pressure gauge starts fluctuating until it eventually
just dies (when it gets warmed up). It can sit for a
bit and cool back down then it starts right back up
and does the same thing once it gets warm again.
I’ve been told to replace the oil sending unit but I
just wanted some feedback before I put any more
money into it