Is there a need to adjust when shooting downhill? I hunt NW Missouri and am ground hunting on top of a bluff. I would guess its a 30ish degree slope. I have missed 2 times in a row now, different days. Also, I am able to rest on a fallen tree so I have felt good about both shots. I would say the shot distance is 80 to 100 yards. Should I be aiming differently when shooting downhill like this? Thanks!

At just 100 yards, I highly doubt it.
Bear in mind it's incredibly easy to overestimate how sheer the angle is. I don't know why.

Put simply, at a hundred yards and a 30% slope you are effectively shooting 90 yards (actually 87). The difference in bullet strike is going to be maybe an inch high, not enough to miss a whole Deer.

Depends on velocity and other factors but the 87% is a constant for a 30% slope. Your effectively shooting 90 yards (or 69 yards if it is a 80 yard shoot).

When is the last time you took your rifle to the range to check poi?

With archery, if your shooting up or down hill, your going to hit high. But with a flat shooting rifle, not so much; I've shot up and down hill with my 3006 and still hit the POA.

I shot a week ago and was hitting about 2 inches high, but I was at 60 yds and I am zeroed in a 100 so I figured that's why I was hitting high. I just zeroed in today at a 100 again. I appreciate all the feedback. I guess it comes down to, I just missed. Thanks all

You'll hit high with a rifle too - but usually nobody shoots far enough for the shift to make much difference. It's just too difficult in most states to find a clear line of sight with significant grade far enough to matter. At 100yrds, there is no angle a guy could shoot to completely miss a deer because of the angle.

The true horizontal range is the measured LOS * cosine(angle). So if you're shooting 400yrds down a 25degree grade, that's really only 360yrds, and with a 30-06 (150grn, .446BC, 2950fps), that's a 7" miss over the POA.

At 100 yards with a modern rifle no adjustment in needed. Hold dead center and get the skinning knife ready.