IPad sucking up cell data at an alarming rate

Question

Hello,
This issue has been driving me crazy for about six months now, I could really use some help in nailing this down.
It appeared to start last Fall, around October. I started to notice that my iPad's cellular usage had increased dramatically. I had been buying 1GB at a time, and it had been lasting me 10-12 weeks. Now it seemed I’d go thru 1GB in two weeks. Generally speaking, the balance of my iPad use between “on WiFi’ and “on cellular” hadn’t changed. The only things systemically that had changed was I had become active on Twitter and Google+, and iOS 8 had been released.
The first thing I did was shut off cellular usage for Twitter and Google+, but that didn’t make a difference. Indeed, as I studied the problem (it was hard to ignore), I noticed that frequently, while doing nothing with my iPad, it just sitting in my bag with the cover closed as I drove from one place to another, I’d use up 10-15MB in 20 minutes.
When I looked at the cellular usage statistics in Settings, “Documents and Sync” (which could be more vague, but it would take some effort) seemed to be where the biggest usage was. I spoke with an Apple Store Genius, and while she couldn’t find a specific culprit, she recommended I reset my iPad and then restore from a backup. That seemed to help, in that I went thru 1GB in a month rather than two weeks; but I still got that weird effect where I would use up a huge chunk doing nothing. I started turning off cellular usage for anything for which it wasn’t essential, did the same for location services, background app refresh, and shut off Find My iPad. Not a noticeable change.
About a month ago, I bought a new iPad Air 2 (I was gonna do that anyway). I was really hoping it was some hardware thing on my old iPad, and the new one would be OK. I built the Air 2 up as new (i.e., not from the backup of the old one), even gave it a new, unique name. But I still find it using dozens of MB doing nothing when I spend any time away from WiFi.
But not always, and that’s the inconsistent, hardest to understand part. A good example was yesterday. I had an errand to run that involved making the same 25-minutes-in-each-direction drive, once in the morning and again in the afternoon. In the morning, I used my iPad to listen to a radio station stream. When I got home, I had used up about 8MB (that actually seemed low, to be honest). When I did the second trip in the afternoon, I took my iPad, but it was in my bag, with the cover on, the whole way. When I got home I’d used up 50MB.
The thing that’s kinda bugging me in the back of my mind is that he only things consistent through all the various attempted solutions and iPads, are iOS 8 and my iCloud account. I can’t help feeling something syncing to iCloud (or some other iOS 8 thing) is the cause of all the extra usage. (At one point, I thought Safari was responsible; I notice that the spinning gear in the status line seems on whenever Safari is active, even after the page I'm viewing apparently completes loading. I shut off cellular for Safari, but it didn't seem to fix it. If someone can address this, I'd appreciate it as well.)
Can anyone offer any advice at all? I would really like to find some way of stopping, or at least slowing down, this apparently-excessive cellular usage. Or at least understand where it’s coming from. I’m sophisticated enough to follow diagnostic instructions, Terminal-friendly, etc., so if there’s some tool I can use on my iMac when my iPad’s plugged in, or some such, I should be able to handle it.
Thanks.

Answer 1

OK, someone needs to explain this to me. Seriously.
If you read my posts, you may infer that in the back of my mind has been the annoying suspicion that this was somehow an iOS/iCloud issue, based on the timing (the problem appeared just last fall, almost immediately after iOS 8 was released), and the persistence despite restore/rebuilds and even a new iPad.
iOS 8.3 was released April 8. My "incidental" cellular usage dropped precipitously immediately afterwards. Look at this, my cellular usage for April, according to Data Usage:
I had to truncate the y-axis at 10MB or you couldn't see the smaller bars. Here's the table:
4/1
5.04 MB
4/2
2.76 MB
4/3
78.97 MB
4/4
4.45 MB
4/5
21.25 MB
4/6
2.61 MB
4/7
40.33 MB
4/8
24.97 MB
4/9
0.05 MB
4/10
0.27 MB
4/11
1.19 MB
4/12
0.32 MB
4/13
0.14 MB
4/14
8.95 MB
4/15
0.22 MB
4/16
0.13 MB
4/17
0.89 MB
4/18
0.29 MB
4/19
0.07 MB
4/20
0.12 MB
4/21
0.15 MB
4/22
36.95 MB
4/23
0.76 MB
I don't want to jinx it, but it looks like something in the 8.3 release fixed my problem, whatever it was. This is the kind of usage I'd been used to seeing through last Summer.
So. Is there someone out there who reads this and is (a) familiar enough with iOS to understand how and when cellular data is consumed, and (b) is familiar enough with the 8.3 release — and the changes it comprised — to take a shot at explaining what may have been going on?
I'm happy to just shut up and accept that it's fixed , but I am curious.
Thanks.
Jeff