Chuggling at 70 mph

I have '98 Transport Montana and I took it on a trip last weekend on the expressway. I would be doing 70 MPH and approach a hill and start depressing the accelerator to maintain my speed and I could feel a chuggling, fishbite kind of feeling. Also, I could hear the engine seem to make a change in its sound coincident with the chuggling. The RPMs at this point were around 2K. I have no codes. I was wondering if anyone knows where to look. It's a 3.4 and all of the normal stuff has been maintained properly (spark plugs, filters, etc.). Thanks.

Sure you are not feeling a misfire?

Only way to know whether to know for sure, would be a road test with a scan tool, like a Tech II attached....

You watch transmission slip data and misfire data when the problem occurs to determine if the problem is in the tranny or engine......but like I said, sounds more like a misfire.....

Sure you are not feeling a misfire?

Only way to know whether to know for sure, would be a road test with a scan tool, like a Tech II attached....

You watch transmission slip data and misfire data when the problem occurs to determine if the problem is in the tranny or engine......but like I said, sounds more like a misfire.....
I never considered that possibility, but I guess it could be. I changed the spark plugs a while ago. Perhaps it's due for another thorough tuneup. Thanks. 162,000 miles.