You say that the temps vary a lot in the mash tun? Are we talking like 5º swings? if that is the case what would you recommend doing to keep it consistant? For my first brew I pulled off a coulpe of quarts and kind did a manual recirculation. I did this about every 25 min for 90 min. I also gave it a stir 2 times. I lost 2º in doing this but I wasn't worried beings the sugar profile should have been set in the first 10 min or so.
My system only varied by 2-3 degrees prior to pump recirculation and brewing in the warmer months of the year. It does take a couple batches to get used to the new system and it is easy to over compensate during temp swings. I would use an extra lab thermometer to check temps in other parts of the mash tun.
After adding a pump, I found the mash would drop about 4-5 degrees during recirculation. I tried direct fire mash recirculation, but had to be careful not to heat it too much - the temp keeps going up after the burner is off. I think the temp of the wort below the false bottom cools off faster than the mash and it heats much faster with direct fire. So, I am pleased with the addition of the heat exchanger in the HLT. Now I know the temp of the wort returning to the mash and the actual mash temp, so it is more predictable.
Cheers!

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