Auto-Trans High Mileage Jerking In 3rd When The Accelerator Is Pressed Hard?

I have a 93 AWD Aerostar extended minivan that has about 155,000 on it. The Trans was rebuilt at around 30,000 from Ford on a warranty from the previous
owner.
Getting to my problem, recently I have noticed that only in third gear I get the jerking (feels like jerking from being in the wrong gear while driving a manual) when I step on the gas to pass or climbing hills etc. First and second do not have this phenomenon while in drive or manually shifting with the lever. I have noticed the occasional clunk when I take my foot off the gas and then depress again but this doesn't happen very often.
I have checked the fluid, levels are ok but the fluid smells a tad burnt. I have read that it's not a great idea to change fluid on a tranny that has high mileage especially if they haven't been routinely maintained. My final question is should I change the fluid/filter and if so will it do anything.
This last month has been a very interesting one, new plugs, new muffler, new brakes all the way around, new shocks all the way around, and a new starter.fun fun fun!!! I can't begin to imagine how much I would paid if I didn't do the work myself. Boy are minivans fun to work on!
Any help or info would be greatly appreciated!!!
4:20
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Just got done with the Trans oil change.the oil was defiantly dirty and smelled a little burnt. I didn't see any metal shavings on the magnet attached to the oil pan, isn't this considered a good sign or am I just reading to much into it(my first time:)? Also I noticed that all the little gears and everything else on the under side looked rather clean and rather new.
The oil defiantly had been changed before because the old gasket was completely in tact no wear what so ever. I also know the previous owner who was very meticulous about maintenance
The

previous
get
a
with
I
final
anything.
new
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.