01 Blazer hesitation

I saw an earlier post with a similar problem, and posted there but got no responses. I'll try again with more details. Can anyone help please:

I have an 01 Blazer with about 40k on it. At a constant highway speed, there is a very slight, but very regular (every 5-25 seconds) hesitation. It is just barely noticable. First time I felt it, it took me a while to realize it wasn't just wind resistance or from road surface. After turning everything off, etc... I discovered that it didn't occur when the Air Conditioning is off. Always occurs when the air is on. Later I discovered it also happens when the defrost is on. Since my last post can say that it doesn't happen when the heat is on. I can only feel the hesitation at highway speed because it is so subtle, but believe it happens at all speeds when air/defrost is on.

I have also noticed that it is shifting late/hard in the first and second shift. Seems to shift later/harder when air/defrost is on, but also does it when everything is off.

Does anyone have any ideas on this? Could this be just one problem causing both the hesitation and the late shift? Or do I have two problems, with the hesitation compounding the late shift problem?

Any help is greatly appreciated!

Since the hesitation happens with the A/C on and also when the defroster is on (A/C compressor runs in defrost) I would say you are feeling the A/C compressor clutch cycling.
This might be a normal operation or the refridgerant level is a little low causing the compressor to cycle more than normal.

My 99 is doing the exact same thing. I first thought it was stumbling badly from a miss or something, but it is directly tied to the a/c compressor coming in and out. It feels like it has no power when it pulls in. Is this a normal Blazer quirck?