OM (I don't want to call you Mr. Freak) --
I should have asked how are you measuring power? If for example you are measuring on a 50 or 100 watt scale - I would not trust the accuracy on the extreme low part of the dial.
We should wonder if your rig is really outputting more power than you think is being measured? Its actually pretty hard to reduce its power by a couple dB with circuit issues!
Do measure your Power Supply voltage while transmitting ! If it is pulled down below 13 or 12 volts, the output power will go down. its related to the square of the bias voltage on the finals.
I am fortunate to have a WM2 wattmeter - its not perfect, but reasonable. Its designed for QRP. A decent power measurement can be made with a diode detector. W7ZOI describes this method, and I have a widget for doing it. It works nicely. You need a 50 ohm dummy load (I used a couple 100 ohm 2 watt resistors in parallel) followed by a silicon diode in series, and there is a shunt capacitor I can't recall the value. Then measure the voltage here at the output with a DVM - and its as easy conversion to power. If you email me, I could dig to find the info.
Your lab is quite good ! Most hams use only simple test equipment, and some of it can be homebrewed.
A ham license is a life-long learners permit. Don't fret but enjoy the journey. See I learned something as I did not ask you enough questions !
This is a cool rig, owned by thousands around the world.