I think similar to you it has become slightley less effective. However I am still getting good pumps.
The fact I was over training and doing a lot of dropsets might have had something to do with the amount of pump I was getting. You get a good pump from dropsets anyway let alone with a pump supplement!
I still get a good pump. Energy levels are still high come the end of a workout. I could up the dosage if I liked. I think it's started to taste a little different too. The fact I'm getting extra amino's and proteins to my muscles when I need them is reason enough for me to continue taking it until this tub's done.
I've made a 3-4lb gain in weight but that was more so over the last 2 weeks due to upping my calorie intake and a change in a few exercises. My stretch marks on my armpits/chest are shifting too and my legs are coming along nicely and my upper back is filling out so I'm still growing and not gaining it just as fat.
I deffinately find that the last few reps I would struggle with become easier. And I can battle through the point of stalling, albeit very slowly, but none the less push through it
I get my samples from the guy I buy most of my supplements from. Are there none on the Phd website? or competitors websites? I found a site doing it for £29.99.
I think the recommended period off pump supplements is a bit longer than 2 weeks probaly more like 4.