Newbie heart rate and Lactate threshold questions.

I decided in January I wanted to get in better shape and vowed to do a Triathlon, so I began training the 3 different disciplines and by today I had entered and completed two 5K's and a sprint tri. I trained almost exclusively by perceived exhaustion and thought I was doing Ok even though I was never able to run further than 3.5-4.0 miles.

Hoping to do better this year after learning how important heart rate training was, I recently had a Max VO2 test done in a lab and found my lactate threshold to be very low (HR 143) while my Max HR was 196.

I found all of my training was indeed too hard and I had ripped down precious lean body mass and raised bodyfat levels when comparing to my last evaluation.

To make a long story longer, I have found it impossible to run at a heart rate even close to 142. I start my runs with a mile walk to stabilize my hr at about 117-121 but as soon as I start jogging painfully slow my heart rate jumps to 152, 158, 162 and levels at 164 until about 3 1/2 miles to where it climbs to 172 and I am done running.

I am 39, 5 10, 188lbs and do want/need to drop down to 170

I guess my question is am I too ambitious for the shape I am currently in?
And is there any way to raise lactate threshold limits faster than at glacial speeds? Or s hould I just resort to biking where I can control my HR until I get in better shape?

I wish I could say Toss the HRM away and carry on but I have already seen how detrimental that course of action has been for me.