You're probably right.
The real problem is the TD04 on a 2.5L. Of course 4th and 5th gear are going to cause problems.
A lot of tension on the WG arm is a band-aid. And not a good one. I think the stock spring is 6-8 lbs if that. If you start cranking down on the spring your control resolution disappears especially with the stock BCS. How many miles on it? A new actuator might help. They do wear out.
Take a good tune off for a crap one. Not sure why you'd expect good results.