Update...I just did a dummy booking for you, and the total comes to $3,012 with all taxes. I think this is pretty much the cheapest you are going to get.

By the way, you're going to be on a plane for a looooong time!

Here is the routing:

Itinerary

Houston (IAH) to Dushanbe (DYU) - Thu, Sep 18
Turkish Airlines Inc. Houston (IAH) to Istanbul (IST) - Thu, Sep 18
Turkish Airlines Inc. 34 Dep: 8:00PM Arr: 3:45PM 11h 45m Boeing 777 Economy (H)
Layover in IST Fri, Sep 19 53h 25m

Turkish Airlines Inc. Istanbul (IST) to Dushanbe (DYU) - Sun, Sep 21
Turkish Airlines Inc. 254 Dep: 9:10PM Arr: 3:45AM 4h 35m Airbus A321 Economy (H)
Mon, Sep 22

Dushanbe (DYU) to Kuala Lumpur (KUL) - Thu, Sep 25
Turkish Airlines Inc. Dushanbe (DYU) to Istanbul (IST) - Thu, Sep 25
Turkish Airlines Inc. 255 Dep: 5:40AM Arr: 9:05AM 5h 25m Airbus A321 Economy (V)
Layover in IST 16h 10m

Turkish Airlines Inc. Istanbul (IST) to Kuala Lumpur (KUL) - Fri, Sep 26
Turkish Airlines Inc. 60 Dep: 1:15AM Arr: 4:50PM 10h 35m Airbus A330 Economy (S)

Kuala Lumpur (KUL) to Houston (IAH) - Sun, Sep 28
Turkish Airlines Inc. Kuala Lumpur (KUL) to Istanbul (IST) - Sun, Sep 28
Turkish Airlines Inc. 61 Dep: 11:15PM Arr: 5:35AM 11h 20m Airbus A330 Economy (T)
Layover in IST Mon, Sep 29 7h 30m

Turkish Airlines Inc. Istanbul (IST) to Houston (IAH) - Mon, Sep 29
Turkish Airlines Inc. 33 Dep: 1:05PM Arr: 6:05PM 13h 0m Boeing 777 Economy (T)

Cost per passenger (including taxes & fees) $3,012.00
Total cost for 1 passenger $3,012.00

And here is the fare construction that you should give to your travel agent:

Fare 1: Carrier TK HLV3XPX HOU to DYU (rules)
Passenger type ADT, round trip fare, booking code H
Covers IAH-IST (Economy), IST-DYU (Economy)
$1,039.00
Fare 2: Carrier TK VXPX2YY DYU to IST (rules)
Passenger type ADT, round trip fare, booking code V
Covers DYU-IST (Economy)
$278.77
Fare 3: Carrier TK ST2XEX IST to KUL (rules)
Passenger type ADT, round trip fare, booking code S
Covers IST-KUL (Economy)
$482.74
Fare 4: Carrier TK TLV3XPC KUL to HOU (rules)
Passenger type ADT, round trip fare, booking code T
Covers KUL-IST (Economy), IST-IAH (Economy)
$282.50
Turkish Int'l Airport Service Charge (TR) $28.60
TK YR surcharge (YR) $818.80
US International Departure Tax (US) $17.50
US September 11th Security Fee (AY) $5.60
US Passenger Facility Charge (XF) $3.00
USDA APHIS Fee (XA) $5.00
US Immigration Fee (XY) $7.00
US Customs Fee (YC) $5.50
US International Arrival Tax (US) $17.50
Malaysia Passenger Service & Security Charge (MY) $20.50

Subtotal per passenger $3,012.00
Number of passengers x1

TOTAL AIRFARE & TAXES $3,012.00

This ticket is non-refundable.
Changes to this ticket will incur a penalty fee.

Fare construction:

HOU TK IST TK DYU 1039.00HLV3XPX TK X/IST 278.76VXPX2YY TK KUL 482.74ST2XEX TK X/IST TK HOU 282.50TLV3XPC NUC 2083.00 END ROE 1.00 XT 5.50YC 7.00XY 5.00XA 35.00US 5.60AY 28.60TR 20.50MY 818.80YR 3.00XF IAH3.00