okay, my 2000 chevy astro (automatic trans) has 164,000 miles on it. when i tow using the tow/haul mode and put the gear selector in "3" as per the manual, then on the highway i put it into "D" and leave tow/haul mode on, also per the manual. when i step on the gas when towing, after coasting, like going down hill or on a low speed road, the engine rev's a bit, almost like it was in neutral. Then after a second it catches, it goes into gear, but the engine revs pretty high before shifting and can have hard shifts going uphill or at 50MPH. i checked the trans fluid last week and it was way low, so i have been slowly adding some over the past few days, and it is now in the acceptable range. but i don't thing that the shifting is directly related to the low fluid level, as other's say their chevy's with tow/haul mode do this. it never does this when just driving, is there someting to be concerned about?