Glad to hear the effexor is helping. To my understanding, Cymbalta has a shorter half life and quicker "plasma" build, therefore its essentially quicker and more potent in effects. In this respect, its kind of like tramadol but with stronger SNRI properties but no Mu Opioid properties. However, Effexor is still a relatively potent SNRI anti depressant, so I can see it being both helpful for pain and that it helps with withdraw too.
I'm on Nucynta (tapentadol) which is a low end of moderate stregnth mu opioid receptor agonist (stronger than tramadol, weaker than oxycodone on THAT specific action) but its a moderately potent NRI. Less so than Cymbalta, but enough so that it makes a considerable contribution to pain relief so that the opioid properties can afford to be weaker.
The good thing with opioids with dual/tri action and anti depressants is that they build tolerance slower than traditional opioids and seem to work fairly well for nerve pain. Not exactly good agents for break through pain, but well suited for chronic around the clock relief. The biggest drawback is some of the side effects (like sleep issues) and that withdraw (especially with the dual/tri action opioids) can have some emotional related effects.
Also, not sure if you were aware of this Jim but Effexor has very mild Mu opioid agonist properties. Its chemically related to both tramadol and Nucynta (tapentadol) but has less opioid action than both, so its generally not viewed as being an opioid in that regard.
In my humble opinion and from what I've read up concerning the medication and their effects:
Effexor: very weak opioid, moderately strong SRI, moderately strong NRI, weak DRI
Tramadol: weak opioid, moderate SRI, moderate NRI, very weak DRI
Tapendtaol: moderate opioid, moderately strong NRI, weak SRI, no direct DRI action