Is my transmission going bad? shifts at higher RPMs then before
 

I have a 03 Chevy Suburban with about 78000 miles.

My wife had the Suburban up at her families, out-of-town. About 2 weeks ago, my father-in-law changed the plugs while she was visiting them. On the way home, the check engine light came on. Concerned, she took it to the dealer. They said a spark plug wire was bad. While they were looking at it, they also changed the fuel filter.
I am not sure if the following symptoms are a result of any of the services done in the past 2 weeks (new plugs and a new spark plug wire/cable) or if its just coincidence. Now, the Suburban seems to struggle when shifting. It stays in a gear for a longer period of time before shifting. I am not positive of the RPMs it reaches before it shifts, but I know if it is rev'ing up more on the RPMs before shifting then a few weeks prior. Today, it started feeling sorta sluggish as we are going down the road, alsmost as if we were towing a heavy load, and the load was going forward and backward, or as if I was carrying a load of water, and water was swishing forward and backward. I am not sure if its a spark issue, timing, or a transmission problem. Some relatives suggested that I have the transmission system flushed and changed at a dealership. I really don't have the time or tools to do it myself. I haven't ever had the transmission flushed, so I am sure I am long overdue for that and it needs to be done regardless. However, I am concerned that I may have a transmission going bad.
1. Do you think I have a transmisison issue beyond the need to change and flush the system?
2. Do you think these issues are related to the plugs, either wires/cables, or other?
3. A relative said I ought to take it to a dealership to have it flushed, as they have better equipment, etc. My experience is that dealers usually charge more for the same service. Is this something that merits having the dealer do it, or would any service place that changes/flushes a transmission be sufficient?
Thanks in advance,
KCP

RE: Is my transmission going bad? shifts at higher RPMs then before
 

For what it's worth, my transmission mechanic says transmissions don't need flushing, they only need regular fluid and filter changes. He says he's seen many transmissions go bad after flushing.

RE: Is my transmission going bad? shifts at higher RPMs then before
 

That advice is worth about as much as you paid for it.;)

RE: Is my transmission going bad? shifts at higher RPMs then before
 

My '03 was doing something similar. When shifting from 1-2 it hesitated before locking (slower to shift) and in 2-3 and sometimes 3-4 shifts it wouldn't shift unless I let off the gas a little which forced it. The dealer just replaced the pressure control valve in the transmission rather than doing another flush and it's now fixed. This was going on for over a year now so I'm pretty happy. Hope that helps you.