2006 Impala - 4T65-E shifting issue

DD#2 reports that her 2006 Impala (3.5l) has started hanging in third for a while before finally shifting up the fourth.  She said it shifts up to fifth just fine, but since it is a 4-speed box, I'm assuming that she's referring to TC lockup.  She's not mechanically inclined.

She said it will run out to 3,500 or 4,000 rpm before finally upshifting, which is not normal to the car for her driving profile.

Car has about 75,000 miles I believe.  No data on if it's ever had a fluid change - it has not during our ownership.  We bought it with just under 50,000 on the clock.

Is this a typical thing for the 4T65-E?

Will a drain and fill help / fix it?

It will have to be handled by her via a local shop because I am 600+ miles away from the car.  Thanks in advance for any info.

I have a 2005 Impala and it was doing kinda the same thing. Put in a can of Seafoam and ran it a couple hundred miles then changed the fluid and filter.  Drove it from Arkansas to Buffalo, N.Y. and back with no problems.  It is starting to act up a little bit again after a few months.  May have to fix/replace the transmission or replace the car. 

In reply to Duke :

Is she still in South Indianapolis?  We might have some good guys on the ground there who could recommend...

In reply to John Welsh :

Yes, indeed, she is, and recommendations will be greatly appreciated.  Thanks!

At the most basic, has trans fluid level been checked?  

John Welsh said:

At the most basic, has trans fluid level been checked?  

I told her how to do that.  She just got back in town after visiting us, so I will remind her.  Thanks.

DEXRON-VI is current for GM transmissions, correct?

Bump!  Anybody with advice or transmission shop recommendations in Indy?

Thanks!

Definitely change the fluid and see if that helps.