PNM transmission lines on the West Mesa. (Greg Sorber/Albuquerque Journal) ALBUQUERQUE, N.M. — Public Service Co. of New Mexico and energy giant Avangrid are doubling the amount of rate relief they plan to offer utility customers, plus other benefits, to gain Public Regulation Commission support for their proposed merger. The companies filed an “initial stipulation” agreement on Wednesday at the PRC outlining a range of concessions negotiated with some of the intervenors in the merger case, which is scheduled for public hearings in early May. The companies propose to double the amount of rate relief paid to PNM customers over three years, from their initial offer of $25 million when they filed last November for PRC merger approval to $50 million now. If divided among 530,000 PNM customers, that would amount to about $94.35 per ratepayer, or about $31.45 per year, through a monthly credit on bills totaling about $2.62 per month.