Just to make sure I understand the situation:
1) You are using full version of uShop 3.x? (YES/NO)
2) The customer is able to see/fill out the uShop 3.x order forms? (YES/NO)
3) The customer successfully receives the email receipt? (YES/NO)
4) The storeowner successfully receives the email notification? (YES/NO)
5) And the only problem is that the final "Thank You" page is not being displayed? (YES/NO)
Assuming the answer is "YES" to all of the above questions....
There is really not much that is done after the point where the emails are sent ... other than to read the receipt template and output the HTML.
Here are two things to try:
TRY 1) On your uShop 3.x Control Panel - Under "GENERAL SETTINGS -- ORDER FORM SETTINGS", make sure you have the same value/file name specified for the fields "Order Form Template 1", "Order Form Template 2", and "Order Form Template 3".
TRY 2) If that still does not work, Under "GENERAL SETTINGS -- MISCELLANEOUS", set the following three fields:
Maintain Customer Log: NO
Maintain Inventory Log: NO
Thank You Page: YOUR URL
(Where "YOUR URL" is actually the main URL of your website ... or any valid URL for that matter.)
If these suggestions do not resolve the problem and/or if I missunderstood the situation, send us a support request with your details... and if possible, the results of a diagnostic report (On the uShop 3.x control panel press "DIAGNOSTICS").