Roger I went and have been searching for a fix for your issues and I have found a few cases that might pertain to your seatbelt tightening up and locking.
Vehicle IssueSeatbelt warning lamp on; SCTM failure code => Replace seatbelt control timer module;In what area is the electrical problem? >> Passive restraints What is the code in the airbag module? >> SCTM failure What is the problem with the passive restraints? >> Seatbelt warning lamp on, code in airbag control module
System or ComponentCustomer Concern (No DTCs);Seat Belt Reminder Light,Passive Restraints
Recommendation Replace seatbelt control timer module
Vehicle IssueThe seatbelt light comes on; the seatbelts may lock up. There is a code in the AECM for a " SCTM failure". 1998-1998 BR/BE.;This is not to be confused with a seatbelt light that comes on and there is NO codes in the airbag (aecm) module, if so then this case does not apply. Usually the code and lamp is extremely intermittent. This case applies to 1998 & 1999 BE truck only.
System or ComponentActivates / Operates by Itself / Ghost Cycle,Flickers / Flashing,Will Not Turn Off;Customer Concern (No DTCs),DTC / Error Message;SCTM,Seat Belt Reminder Light,Electronically Controlled / Motorized Seatbelts,Seat Belt / Shoulder Belt;Interior;Yes - Intermittent,Yes - Continuously,No - Condition Never Duplicated
RecommendationCheck pins 4-5 (+), pins 6-13 ground, pin 11 (g111). The code will set if the g111 does not have between 1-3 volts. Also be sure the solenoids will lock up and are plugged up. Check the C360 and c203 connector. See page 83 of the 1998 green body book, it has some good diagnostics as well a good circuit description. If the SCTM is lost the AECM will turn on the light. Also make sure the solenoids work properly, if unplugged the seat belt light will come on. Check the wiring in the left kick panel and left side of column area. Check c360 and c200 connectors.
Modification Date08/13/03 10:25 AM
Vehicle IssueThe seatbelt light comes on and the solenoids retract. This happens when you go 25 miles. The technician can open the door and close it and the light would go off. The SCTM, both retractors, CTM and ACM may have been replaced already.
System or ComponentActivates / Operates by Itself / Ghost Cycle;Customer Concern (No DTCs);SCTM;Right,Left;Yes - Continuously
RecommendationIgnition sense wire at the Seat belt control module is either pushed out, the terminal is spread or the crimp is not holding all of the strands of wire. (Bad connection)
Modification Date05/13/04 1:17
At this point I would have the codes checked in the Central Timer module as well as the airbag module. If there are any codes I would run the diagnostics to find your issue..