hashimoto's and low heart rate post treatment

My 15 yr old son was dx as hashimoto's with secondary hypo 10/24/2006, we took him to the pcp because he was having tremors, headaches and dizzy spells. His Tsh was 10.341 so they refered him out to a endro . It took six weeks to get  his appointment with her, his TSH was then 18.50 was started on synthroid 0.1  at that visit his heart rate was then 88 BP was 138/88

Next visit 1/04/2007 his TSH was 34.3 and FT4 was .51 his heart rate was then 64 his BP was 122/78 his synthroid was upped to .137 At his 6 week blood draw she upped his dose to 0.15

Visit 3- 05/03/2007 - His TSH was  3.7 heart rate of 60 BP 122/72  synthroid was upped to 8 pills per week vs. 7

Visit 4-8/29/2007- TSH 2.4 heart rate of 52 blood presure of 116/80 upped does to .175 7.5 tablets a week

Visit 5- 10/8/2007 TSH 1.70 FT4 .67 heart rate was 47 blood pressure 124/76 still the same dose of synthroid.

My question is this, I know heart rate problems are " normal" in hypo pt's however everything I have read says that should resolve with hormone treatment and his has not. His did not start to slow down till AFTER treatment.

He has had a 48 Holter moniter test that was found to be normal except for the low heart rate which was a average of 46 bpm.

His endro is saying this is a heart problem not hypo, and his PCP is saying it is an endro problem. Should we seek the advice of a cardologist? I am real concered about this since he is still having the tremors and dizzy/and now fainting spells upon rising that he was having a year ago.