In addition to the contribution from the Vesta acquisition, our rental operations experienced strong organic growth across our commercial, education and portable storage customer bases. Sales revenues increased $29.9 million to $58.9 million demonstrating good progress with our initiative to grow modular sales projects. Vesta contributed $16.2 million or roughly half of the increase. We continued our disciplined fleet management on a much larger fleet and achieved a 30% higher average rental equipment on rent with average fleet utilization of 79.4%, down from 80.1% a year ago. Keep in mind that we have achieved this healthy total fleet utilization, while integrating Vesta’s fleet, which was utilized in the mid-70s at time of acquisition. The average monthly rental rate for the portfolio was 2.92%, which was 5% higher than a year ago and reflects our focus on pricing optimization as well as continued healthy market conditions.
Rental revenues increased by 36%, while inventory center costs increased 2% and depreciation expense increased 30% resulting in rental margins of 65%, up from 56% a year ago. Similar to last quarter, I will share additional data that helped illustrate our progress with our modular business strategic focus. Third quarter monthly revenue per unit on rent increased year-over-year from $633 to $695, a 10% increase. For new shipments over the last 12 months, the average monthly revenue per unit was $1,027. A year earlier, this last 12-month average revenue was $905. So, we see a positive trend with new unit pricing, which is up 13% on a full year-over-year basis. Similar to last quarter, this data is for our legacy modular building and classroom fleet, excluding Vesta.
These pricing dynamics are significant, positive long-term revenue drivers. As the rental fleet churns, we expect a rental revenue tailwind as the average rental unit pricing for all units on rent moves towards current market rates. Our early progress with Mobile Modular Plus is embedded in these data points and is an additional growth opportunity for us. We continue to make progress with our modular services offerings for our legacy modular business, excluding Vesta and Portable Storage. Mobile Modular Plus contributed $20 million revenue year-to-date, up from $13.7 million a year earlier. Site-related services contributed $18.3 million revenue year-to-date, up from $11 million a year earlier. We are in the early innings with these initiatives and they are making positive growing contributions.
Turning to review of TRS-RenTelco, adjusted EBITDA was $21.9 million, a decrease of 9% compared to last year. Total revenues increased point $0.6 million or 2% to $39.1 million. We saw an increase in sales revenues, partly offset by a softening in rental operations revenues. Rental revenues for the quarter decreased 10%. As we experienced continued softness in semiconductor related demand, the average monthly rental rate was comparable to the previous year, which reflects generally stable pricing conditions for both communications and general purpose equipment in the current market. Average utilization for the quarter was 59.4% compared to 65.3% a year ago and rental margins were 40% compared to 44% a year ago. Sales revenues increased 58% year-over-year to $8.7 million, with gross profit decreasing 9% to $3.1 million due to lower gross margins in 2023.
The increase in sales revenues demonstrates our focus on reducing inventory to better align with current market demand. To address the currently challenging business conditions at TRS, we maintained our return on capital discipline. With our actions to reduce new equipment capital spending, and continued focus on sales of used equipment. We have reduced fleet size, based on original cost of equipment from $398 million at the end of March to $384 million at the end of September and ended the quarter with utilization at 60.3%. The remainder of my comments will be on a total company basis from continuing operations. Third quarter selling and administrative expenses increased $11.6 million to $48.5 million. The addition of Vesta Modular increased selling and administrative expenses by $6 million, which included $1.2 million amortization of intangibles.
