Heat only works when you slam the hood

The blower motor control processor is going out . The blower motor is controlled electronically .
The fuse for this is located in the rear fuse box , under the box seat . HVAC BLO fuse 40amp

HVAC Blower Motor Circuit
GMC Yukon HVAC Blower Motor Won Turn On

Probly bad heatr core or hose has clog

Take the blower out, I have a feeling it's flooded.

Only 4 items in fan circuit I think; Fan motor, ballast speed resistor, switch and fuse. If you can access the single wire connected directly to the motor, you can use a jumper wire to batt + to check motor.

The blower motor control processor ! HVAC BLO fuse #2 30 amp -location ,rear fuse box . It is under the back seat . This is s different GM vehicle ,but still the same as your's.
Chevy Trailblazer EXT Blower Motor Won Turn Off

i beleive you did more than that.? you,ll probably find all have a common earth , chech and remove it , clean with a wire brush and replace, also chance the fuse you removed and replacer reguardless of it,s appearence , ensure its put back in the correct location,peter.

CHECK WHETHER IT IS THE BLOWER ITSELF SEIZED.

TYC Part # 700076 {#19153679, 52498954} AC Condenser Blower Assembly
Front* Stocked in outlying warehouse--shipping delayed up to 1 business day$38.79
ACDELCO Part # 158600
MOTOR,BLO(W/IMPLR) [Wholesaler Closeout -- 30 Day Warranty] (Only 2 Remaining)$39.79
VDO Part # PM3799
w/Blower Whl. (Only 2 Remaining)$41.79
FOUR SEASONS Part # 35352
w/ Wheel; Use when replacing a two terminal motor$48.99
ACDELCO Part # 1581104 {#1580467, 19153679, 52498954}
MOTOR,BLO (W/IMPLR) 4 DOORS$51.89
ACDELCO Part # 1580467 {#52498954}
MOTOR,BLO(W/IMPLR) 4 DOORS [Wholesaler Closeout -- 30 Day Warranty] (Only 3 Remaining)$64.79

there is a high blower fuse, check that first. fuse box under the hood marked HI BLO MOT 30 amps. if thats ok, maybe the blower relay is bad. marked HVAC BLOWER .....the lower sppeds use one fuse, hi speed uses another.

Do you have power at the blower motor? Check the motor resistor as well